U.S. patent number 11,390,794 [Application Number 16/648,270] was granted by the patent office on 2022-07-19 for robust alkyl ether sulfate mixture for enhanced oil recovery.
This patent grant is currently assigned to BASF SE. The grantee listed for this patent is BASF SE. Invention is credited to Thomas Altmann, Gabriela Alvarez Juergenson, Christian Bittner, Michael Bueschel, Kathrin Cohen, Clara Maria Hernandez Morales, Prapas Lohateeraparp, Ashok Kumar Mishra, Hans-Christian Raths, Benjamin Wenzke.
United States Patent |
11,390,794 |
Bittner , et al. |
July 19, 2022 |
Robust alkyl ether sulfate mixture for enhanced oil recovery
Abstract
The invention relates to a process for mineral oil production,
in which an aqueous saline surfactant formulation comprising a
surfactant mixture of at least one anionic surfactant of the
general formula
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M and at least one anionic surfactant of the general formula
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M and a base is
injected through injection boreholes into a mineral oil deposit,
and crude oil is withdrawn from the deposit through production
boreholes. The invention further relates to the surfactant mixture,
a concentrate comprising the surfactant mixture and a manufacturing
process as well as the use of the surfactant mixture and the con-
centrate in the production of mineral oil from underground mineral
oil deposits.
Inventors: |
Bittner; Christian
(Ludwigshafen am Rhein, DE), Mishra; Ashok Kumar
(Singapore, SG), Cohen; Kathrin (Ludwigshafen am
Rhein, DE), Hernandez Morales; Clara Maria
(Ludwigshafen am Rhein, DE), Lohateeraparp; Prapas
(Houston, TX), Raths; Hans-Christian (Dusseldorf-Holthausen,
DE), Bueschel; Michael (Ludwigshafen am Rhein,
DE), Alvarez Juergenson; Gabriela (Ludwigshafen am
Rhein, DE), Altmann; Thomas (Ludwigshafen am Rhein,
DE), Wenzke; Benjamin (Hamburg, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen am Rhein |
N/A |
DE |
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Assignee: |
BASF SE (Ludwigshafen am Rhein,
DE)
|
Family
ID: |
1000006443639 |
Appl.
No.: |
16/648,270 |
Filed: |
September 19, 2018 |
PCT
Filed: |
September 19, 2018 |
PCT No.: |
PCT/EP2018/075345 |
371(c)(1),(2),(4) Date: |
March 18, 2020 |
PCT
Pub. No.: |
WO2019/057769 |
PCT
Pub. Date: |
March 28, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20200216747 A1 |
Jul 9, 2020 |
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Foreign Application Priority Data
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Sep 21, 2017 [EP] |
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17192299 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K
8/584 (20130101) |
Current International
Class: |
C09K
8/584 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2760734 |
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2774318 |
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2790159 |
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CA |
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2791119 |
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Sep 2011 |
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CA |
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4325237 |
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Feb 1995 |
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DE |
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10243361 |
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Apr 2004 |
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DE |
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2432807 |
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Mar 2012 |
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EP |
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WO-2006131541 |
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Dec 2006 |
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WO |
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WO-2010133527 |
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Nov 2010 |
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WO |
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WO-2011045254 |
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Apr 2011 |
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WO |
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WO-2011110502 |
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Sep 2011 |
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WO |
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WO-2011110503 |
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Sep 2011 |
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WO |
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WO-2014095621 |
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Jun 2014 |
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WO |
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Other References
International Preliminary Examination Report for PCT/EP2018/075345
dated Dec. 16, 2019 with Applicant amendments in response to IPRP.
cited by applicant .
International Search Report for PCT/EP2018/075345 dated Nov. 7,
2018. cited by applicant .
Written Opinion of the International Searching Authority for
PCT/EP2018/075345 dated Nov. 7, 2018. cited by applicant .
D. G. Kessel, "Chemical flooding--status report", J. Pet. Sci.
Eng., vol. 2, 1989, pp. 81-101. cited by applicant .
Melrose et al., "Role of Capillary Forces In Detennining
Microscopic Displacement Efficiency For Oil Recovery By
Waterflooding", J. Can. Pet. Tech , vol. 13, 1974, pp. 54-62. cited
by applicant .
Taylor et al., "Water-soluble hydrophobically associating polymers
for improved oil recovery: A literature review", J. Petr. Sci.
Eng., vol. 19, 1998, pp. 265-280. cited by applicant .
Weggen et al., "Oil and Gas", pp. 37 ff., Ullmann's Encyclopedia of
Industrial Chemistry, Online Edition, Wiley-VCH, Weinheim, vol. 25,
2010, pp. 121-205. cited by applicant .
Zhang et al., "Favorable Attributes of Alkali-Surfactant-Polymer
Flooding", SPE-Paper No. 99744. cited by applicant.
|
Primary Examiner: Figueroa; John J
Attorney, Agent or Firm: Faegre Drinker Biddle & Reath
LLP
Claims
The invention claimed is:
1. A method for producing mineral oil from underground mineral oil
deposits, in which an aqueous saline surfactant formulation
comprising a surfactant mixture, for the purpose of lowering the
interfacial tension between oil and water to <0.1 mN/m at
deposit temperature is injected through at least one injection well
into a mineral oil deposit and crude oil is withdrawn through at
least one production well from the deposit, wherein the surfactant
mixture comprises at least one anionic surfactant (A) of the
general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M (I) and at least one anionic surfactant (B) of the general
formula (II) R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M (II),
where a ratio of anionic surfactant (A) to anionic surfactant (B)
of 99:1 to 51:49 by weight is present in the surfactant mixture,
where R.sup.1 is a primary linear, saturated or unsaturated,
aliphatic hydrocarbyl radical having 16 to 18 carbon atoms; and
R.sup.2 is a primary linear, saturated aliphatic hydrocarbyl
radical having 12 to 17 carbon atoms; and M is Na, K, NH.sub.4, or
NH(CH.sub.2CH.sub.2OH).sub.3; and x is a number from 3 to 25; and y
is a number from 0 to 20; and z is a number from 1 to 30; where the
sum total of x+y is a number from 3 to 35 and the x+y alkoxylate
groups may be arranged in random distribution, in alternation or in
blocks and wherein the aqueous saline surfactant formulation
further comprises a base or a mixture of two or more of these
bases.
2. The method according to claim 1, wherein the concentration of
the surfactant mixture is 0.03% to 0.99% by weight based on the
total amount of the aqueous saline surfactant formulation.
3. The method according to claim 1, wherein the ratio of anionic
surfactant (A) to anionic surfactant (B) is 95:5 to 55:45 by
weight.
4. The method according to claim 1, wherein the aqueous saline
surfactant formulation further comprises a base, which is selected
from carbonates.
5. The method according to claim 1, wherein at least one of the
following conditions is fulfilled: M is Na; x is a number from 3 to
15; y is a number from 0 to 10; z is a number from 1 to 5; the sum
total of x+y is a number from 3 to 25.
6. The method of claim 5, wherein R.sup.1 is a primary linear,
saturated, aliphatic hydrocarbyl radical having 16 to 18 carbon
atoms; R.sup.2 is a primary linear saturated aliphatic hydrocarbyl
radical having 12 to 14 carbon atoms; M is Na; x is a number from 3
to 15; y is a number from 0 to 10; z is a number from 1 to 5; and
the sum total of x+y is a number from 3 to 25.
7. The method according to claim 6, wherein z is a number from 1 to
5.
8. The method according to claim 1, wherein the aqueous surfactant
formulation further comprises a thickening polymer.
9. The method according to claim 1, wherein the underground mineral
oil deposit consists of sandstone and deposit temperature is below
90.degree. C.
10. The method according to claim 1, wherein the aqueous saline
surfactant formulation is prepared from a concentrate comprising
the surfactant mixture as described in claim 1 and at least
softened water and/or a cosolvent.
11. The method according to claim 10, where a) the cosolvent is
selected from the group of the aliphatic alcohols having 3 to 8
carbon atoms or from the group of the alkyl monoethylene glycols,
the alkyl diethylene glycols or the alkyl triethylene glycols,
where the alkyl radical is an aliphatic hydrocarbyl radical having
3 to 6 carbon atoms; and/or b) the concentrate has a viscosity of
<15000 mPas at 50.degree. C. and at 10 s.sup.-1; and/or c) the
amount of cosolvent by weight is equal or lower compared to the
amount of water by weight.
12. An aqueous saline surfactant formulation as described in claim
1.
13. An aqueous saline surfactant formulation according to claim 12,
wherein the surfactant mixture of anionic surfactant (A) of the
general formula (I) and anionic surfactant (B) of the general
formula (II) are produced in that the anionic surfactant (A) and
anionic surfactant (B) are made separately by alkoxylation of
alcohols R.sup.1OH and R.sup.2OH in a vessel followed by sulphation
with sulfur trioxide in a falling film reactor including
neutralization step afterwards and mixed finally.
14. A concentrate comprising a surfactant mixture as described in
claim 1, and further comprising at least softened water and/or a
cosolvent.
15. The concentrate of claim 14, wherein the concentrate comprises
50% by weight to 90% by weight of the surfactant mixture, 5% by
weight to 30% by weight of softened water and 5% by weight to 20%
by weight of a cosolvent, based on the total amount of the
concentrate.
16. The concentrate of claim 14, where a) the cosolvent is selected
from the group of the alkyl monoethylene glycols, the alkyl
diethylene glycols or the alkyl triethylene glycols, where the
alkyl radical is a primary linear saturated aliphatic hydrocarbyl
radical having 4 carbon atoms; and/or b) the concentrate has a
viscosity of <15000 mPas at 50.degree. C. and at 10 s.sup.-1
and/or c) the amount of cosolvent by weight is equal or lower
compared to the amount of water by weight.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a national stage application (under 35 U.S.C.
.sctn. 371) of PCT/EP2018/075345, filed Sep. 19, 2018, which claims
benefit of European Application No. 17192299.0, filed Sep. 21,
2017, both of which are incorporated herein by reference in their
entirety.
The present invention relates to a process for mineral oil
production, in which an aqueous saline surfactant formulation, for
the purpose of lowering the interfacial tension between oil and
water to <0.1 mN/m at deposit temperature, is injected through
injection boreholes (injection wells) into a mineral oil deposit,
and crude oil is withdrawn from the deposit through production
bore-holes (production wells). The aqueous saline surfactant
formulation comprises a surfactant mixture at least one anionic
surfactant of the general formula
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x-(CH.sub.2CH.sub.2O).sub.y--SO.s-
ub.3M and at least one anionic surfactant of the general formula
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.zSO.sub.3M where a ratio of
anionic surfactant (A) to anionic surfactant (B) of 99:1 to 51:49
by weight is present in the surfactant mixture. The present
invention further relates to the surfactant mixture, a concentrate
out of the surfactant mixture and a manufacturing process as well
as the use of the surfactant mixture and the concentrate in the
production of mineral oil from underground mineral oil
deposits.
In natural mineral oil deposits, mineral oil is present in the
cavities of porous reservoir rocks which are sealed toward the
surface of the earth by impervious overlying strata. The cavities
may be very fine cavities, capillaries, pores or the like. Fine
pore necks may have, for example, a diameter of only about 1 .mu.m.
As well as mineral oil, including fractions of natural gas, a
deposit generally also comprises water with a greater or lesser
salt content.
If a mineral oil deposit has a sufficient autogenous pressure,
after drilling of the deposit has commenced, mineral oil flows
through the well to the surface of its own accord because of the
autogenous pressure (primary mineral oil production). Even if a
sufficient autogenous pressure is present at first, however, the
autogenous pressure of the deposit generally declines relatively
rapidly in the course of withdrawal of mineral oil, and so usually
only small amounts of the amount of mineral oil present in the
deposit can be produced in this manner, according to the deposit
type.
Therefore, when primary production declines, a known method is to
drill further wells into the mineral oil-bearing formation in
addition to the wells which serve for production of the mineral
oil, called the production wells. Through these so-called injection
wells, water is injected into the deposit in order to maintain the
pressure or increase it again. The injection of the water forces
the mineral oil through the cavities in the formation, proceeding
gradually from the injection well in the direction of the
production well. This technique is known as water flooding and is
one of the techniques of what is called secondary oil production.
In the case of water flooding, however, there is always the risk
that the mobile water will not flow homogeneously through the
formation and in doing so mobilize oil, but will flow from the
injection well to the production well, particularly along paths
with a low flow resistance, without mobilizing oil, while there is
only little flow, if any, through regions in the formation with
high flow resistance. This is discerned from the fact that the
proportion of the water which is produced via the production well
increases ever further. By means of primary and secondary
production, generally not more than about 30% to 35% of the amount
of mineral oil present in the deposit can be produced.
A known method is to use techniques for tertiary mineral oil
production (also known as "Enhanced Oil Recovery (EOR)") to enhance
the oil yield, if economically viable production is impossible or
no longer possible by means of primary or secondary mineral oil
production. Tertiary mineral oil production includes processes in
which suitable chemicals, such as surfactants and/or polymers, are
used as auxiliaries for oil production. An overview of tertiary oil
production using chemicals can be found, for example, in the
article by D. G. Kessel, Journal of Petroleum Science and
Engineering, 2 (1989) 81-101.
One of the techniques of tertiary mineral oil production is called
"polymer flooding". Polymer flooding involves injecting an aqueous
solution of a thickening polymer into the mineral oil deposit
through the injection wells, the viscosity of the aqueous polymer
solution being matched to the viscosity of the mineral oil. The
injection of the polymer solution, as in the case of water
flooding, forces the mineral oil through said cavities in the
formation from the injection well proceeding in the direction of
the production well, and the mineral oil is produced through the
production well. By virtue of the polymer formulation having about
the same viscosity as the mineral oil, the risk that the polymer
formation will break through to the production well with no effect
is reduced. Thus, the mineral oil is mobilized much more
homogeneously than when water, which is mobile, is used, and
additional mineral oil can be mobilized in the formation.
Use of hydrophobically associating copolymers for polymer flooding
is known. "Hydrophobically associating copolymers" are understood
by those skilled in the art to mean water-soluble polymers having
lateral or terminal hydrophobic groups, for example relatively long
alkyl chains. In an aqueous solution, such hydrophobic groups can
associate with themselves or with other substances having
hydrophobic groups. This results in formation of an associative
network which causes (additional) thickening action. Details of the
use of hydrophobically associating copolymers for tertiary mineral
oil production are described, for example, in the review article by
Taylor, K. C. and Nasr-El-Din, H. A. in J. Petr. Sci. Eng. 1998,
19, 265-280.
A further form of tertiary mineral oil production is surfactant
flooding for the purpose of producing the oil trapped in the pores
by capillary forces, usually combined with polymer flooding for
mobility control (homogeneous flow through the deposit).
Viscous and capillary forces act on the mineral oil which is
trapped in the pores of the deposit rock toward the end of the
secondary production, the ratio of these two forces relative to one
another determining the microscopic oil removal. A dimensionless
parameter, called the capillary number, is used to describe the
action of these forces. It is the ratio of the viscosity forces
(velocity x viscosity of the forcing phase) to the capillary forces
(interfacial tension between oil and water x wetting of the
rock):
.mu..times..sigma..times..times..theta. ##EQU00001##
In this formula, .mu. is the viscosity of the fluid mobilizing the
mineral oil, v is the Darcy velocity (flow per unit area), .sigma.
is the interfacial tension between liquid mobilizing mineral oil
and mineral oil, and .theta. is the contact angle between mineral
oil and the rock (C. Melrose, C. F. Brandner, J. Canadian Petr.
Techn., October-December, 1974, pages 54-62). The higher the
capillary number, the greater the mobilization of the oil and hence
also the degree of oil removal.
It is known that the capillary number toward the end of secondary
mineral oil production is in the region of about 10.sup.-6 and that
it is necessary for the mobilization of additional mineral oil to
increase the capillary number to about 10.sup.-3 to 10.sup.-2.
For this purpose, it is possible to conduct a particular form of
the flooding method--what is known as Winsor type III microemulsion
flooding. In Winsor type III microemulsion flooding, the injected
surfactants are supposed to form a Winsor type III microemulsion
with the water phase and oil phase present in the deposit. A Winsor
type III microemulsion is not an emulsion with particularly small
droplets, but rather a thermodynamically stable, liquid mixture of
water, oil and surfactants. The three advantages thereof are that a
very low interfacial tension .sigma. between mineral oil and
aqueous phase is thus achieved, it generally has a very low
viscosity and as a result is not trapped in a porous matrix, it
forms with even the smallest energy inputs and can remain stable
over an infinitely long period (conventional emulsions, in
contrast, require high shear forces which predominantly do not
occur in the reservoir, and are merely kinetically stabilized).
The Winsor type III microemulsion is in equilibrium with excess
water and excess oil. Under these conditions of microemulsion
formation, the surfactants cover the oil-water interface and lower
the interfacial tension .sigma. more preferably to values of
<10.sup.-2 mN/m (ultra-low interfacial tension). In order to
achieve an optimal result, the proportion of the microemulsion in
the water-microemulsion-oil system, for a defined amount of
surfactant, should naturally be at a maximum, since this allows
lower interfacial tensions to be achieved.
In this manner, it is possible to alter the form of the oil
droplets (the interfacial tension between oil and water is lowered
to such a degree that the smallest interface state is no longer
favored and the spherical form is no longer preferred), and they
can be forced through the capillary openings by the flooding
water.
When all oil-water interfaces are covered with surfactant, in the
presence of an excess amount of surfactant, the Winsor type III
microemulsion forms. It thus constitutes a reservoir for
surfactants which cause a very low interfacial tension between oil
phase and water phase. By virtue of the Winsor type III
microemulsion having a low viscosity, it also migrates through the
porous deposit rock in the flooding process. Emulsions, in
contrast, may remain suspended in the porous matrix and block
deposits. If the Winsor type III microemulsion meets an oil-water
interface as yet uncovered with surfactant, the surfactant from the
microemulsion can significantly lower the interfacial tension of
this new interface and lead to mobilization of the oil (for example
by deformation of the oil droplets).
The oil droplets can subsequently combine to give a continuous oil
bank. This has two advantages:
Firstly, as the continuous oil bank advances through new porous
rock, the oil droplets present there can coalesce with the
bank.
Moreover, the combination of the oil droplets to give an oil bank
significantly reduces the oil-water interface and hence surfactant
no longer required is released again. Thereafter, the surfactant
released, as described above, can mobilize oil droplets remaining
in the formation.
Winsor type III microemulsion flooding is consequently an
exceptionally efficient process, and requires much less surfactant
compared to an emulsion flooding process. In microemulsion
flooding, the surfactants are typically optionally injected
together with cosolvents and/or basic salts (optionally in the
presence of chelating agents). Subsequently, a solution of
thickening polymer is injected for mobility control. A further
variant is the injection of a mixture of thickening polymer and
surfactants, cosolvents and/or basic salts (optionally with
chelating agent), and then a solution of thickening polymer for
mobility control. These solutions should generally be clear in
order to prevent blockages of the reservoir.
The use parameters, for example type, concentration and mixing
ratio of the surfactants used relative to one another, are adjusted
by the person skilled in the art to the conditions prevailing in a
given oil formation (for example temperature and salt content).
PRIOR ART
WO 2011/110 502 A1 describes the use of anionic surfactants of the
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.m(CH.sub.2CH.sub.2O).sub.n--XY.su-
p.-M.sup.+type, which are based on a linear saturated or
unsaturated alkyl radical R.sup.1 having 16 to 18 carbon atoms, in
tertiary mineral oil production. Y.sup.-may be a sulfate group
inter alia, and X may be an alkyl or alkylene group having up to 10
carbon atoms inter alia. In addition, m is a number from 0 to 99
and preferably 3 to 20, and n is a number from 0 to 99. These
anionic surfactants can be obtained inter alia by reaction of
appropriate alkoxylates with chlorosulfonic acid and sodium
hydroxide.
WO 2011/110 503 A1 describes the use of anionic surfactants of the
R.sup.1--O--(D).sub.n--(B).sub.m--(A).sub.I--XY.sup.- M.sup.+ type,
which are based on a linear or branched saturated or unsaturated
alkyl or alkylaryl radical R.sup.1 having 8 to 30 carbon atoms, in
tertiary mineral oil production. D stands for a butyleneoxy group,
B stands for an propyleneoxy group, and A stands for a ethyleneoxy
group. Y.sup.- may be a sulfate group inter alia, and X may be an
alkyl or alkylene group having up to 10 carbon atoms inter alia. In
addition, I is a number from 0 to 99, m is a number from 0 to 99,
and n is a number from 1 to 99. These anionic surfactants can be
obtained inter alia by reaction of appropriate alkoxylates with
chlorosulfonic acid and sodium hydroxide.
WO 2011/045 254 A1 describes the use of anionic surfactants of the
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x(CH.sub.2CH.sub.2O).sub.y--SO.su-
b.3M type, which are based on a linear or branched saturated or
unsaturated alkyl or alkylaryl radical R.sup.1 having 8 to 32
carbon atoms, combined with surfactant of R.sup.2--Y type, which
are based on a linear or branched saturated or unsaturated alkyl or
alkylaryl radical R.sup.2 having 8 to 32 carbon atoms and are based
on a hydrophilic group Y, in tertiary mineral oil production. In
addition, x is a number from 4 to 30, and y is a number from 0 to
30 and
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x(CH.sub.2CH.sub.2O).sub.y--H
is made by alkoxylation using double metal cyanide catalyst. These
anionic surfactants can be obtained inter alia by reaction of
appropriate alkoxylates with chlorosulfonic acid and sodium
hydroxide.
D. L. Zhang et al. desribe in SPE-Paper No. 99744 (SPE=Society of
Petroleum Engineers) the low salt tolerance of internal olefin
sulfonates. E.g. an internal olefin sulfonate comprising 15 to 18
carbon atoms is soluble at 20.degree. C. in a saline water
comprising two weight percent of sodium chloride. If 0.1 weight
percent of calcium chloride are added, then the olefin sulfonate
precipitates. The internal olefin sulfonate comprising 15 to 18
carbon atoms is not soluble at 20.degree. C. in a saline water
comprising four weight percent of sodium chloride.
US 2016/0215200 A1 describes the combination of an alkyl propoxy
sulfate with a second anionic surfactant out of the group of alkyl
propoxy ethoxy sulfate or out of the group of alkyl ethoxy
sulfate.
OBJECT OF THE INVENTION
There is a need for efficient oil recovery from deposits having
saline deposit water and especially having deposit temperatures of
below 90.degree. C., preferably below 80.degree. C. and most
preferably below 70.degree. C. with surfactant formulations having
the following requirements: surfactant stability; and/or salt
tolerance (water solubility even in the presence of many monovalent
ions, but also polyvalent cations: for example saline water having
divalent cations such as Ca.sup.2+ and/or Mg.sup.2+ ); and/or low
use concentrations (<1 percent of weight, preferably <0.5
percent by weight) in order to keep costs and material consumption
low with a view to sustainability; and/or virtually complete
dissolution in a clear solution at reservoir temperature.
The main surfactant provides typically desired reduction of
oil-water interfacial tension, but it is not clear soluble in
injection water (at surface temperature) and at deposit
temperature. In case, that main surfactant alone is not clear
soluble at surface temperature, then one has to heat the injection
water, which is energy intensive and costly. In case, that main
surfactant alone is not clear soluble at reservoir temperature,
then it can plug the porous media and thereby the injection area.
Addition of a second surfactant can improve overall surfactant
solubility (however, improved solubility usually does not go along
with the desired reduction of oil-water interfacial tension: one
effect is sacrificed by the other effect). In addition, during the
flooding process ratio of main surfactant to second surfactant can
change (e.g. due to selective adsorption or retention). Then, the
solubility of the surfactant formulation has to be still given. For
a surfactant mixture further requirements are important: simple
injection into the porous formation (due to virtually complete
dissolution in a clear solution at reservoir temperature); and/or
good interaction of the surfactants with the crude oil in order to
achieve sufficient reduction of interfacial tension between crude
oil and water (in particular, in case of crude oils, which are rich
in paraffin, it is hard to achieve); and/or low interfacial
tensions at deposit temperature with respect to crude oil (<0.1
mN/m, preferably <0.05 mN/m, more preferably <0.01 mN/m),
even when using only one surfactant (or two very similar
surfactants which differ only in a few aspects--for example small
differences in the alkoxylation level); and/or low adsorption of
all surfactants at the rock surface and no or only minimum change
of surfactant ratio due to selective adsorption or retention of one
surfactant in the formulation; and/or simple production process, in
order to keep the costs of the surfactant formulation low (alkyl
benzene sulfonates or olefin sulfonates can be made easily, but
they usually show low salt tolerance (precipitation); Alkyl ether
sulfates, alkyl ether carboxylates and alkyl ether sulfonates are
much more salt tolerant. However, manufacturing of alkyl ether
sulfonates involves much more steps, which makes alkyl ether
sulfonates very expensive); and/or supply form as surfactant
concentrate which may be liquid at least 20.degree. C. (this would
obviate the need for melting of the concentrate or constant heating
on site and should preferably have a viscosity of <5000 mPas at
50.degree. C. and 10 s.sup.-1 and a high active content in order to
keep the transport costs and the energy consumption resulting from
transport low; and/or it should not have any environmentally
harmful properties (alkylphenol ethoxylates or their degradation
products are known to be able to act as endocrine disruptors).
In this context, particularly the attainment of low interfacial
tensions of <0.1 mN/m and especially <0.05 mN/m, especially
in case of paraffin-rich crude oils is difficult to achieve during
the flooding process with a surfactant formulation.
The flooding process is an industrial scale process. Although the
chemicals used are typically used only as dilute solutions, the
volumes injected per day are high and the injection is typically
continued over months and up to several years. The chemical
requirement for an average oilfield may quite possibly be 5000 to
50 000 t of polymer per annum. For an economically viable process,
therefore, a very high efficiency, i.e. effect per unit volume, is
of great significance. Even a slight improvement in efficiency can
lead to a significant improvement in economic viability.
Consequently, lowering of the interfacial tension between oil and
water to <0.1 mN/m with a low use concentration of surfactant is
desirable (total amount of all surfactants should ideally account
for <1 percent by weight and preferably <0.5 percent by
weight of the aqueous surfactant-containing solution injected. The
injected aqueous surfactant-containing solution is understood to
mean what is called the injected surfactant slug. The surfactant
slug fills a portion of the pore volume and may, as well as the
surfactant, optionally comprise further additives, for example a
thickening polymer. The desired portion of the pore volume may, for
example, be between 2% and 60%, preferably between 3% and 25%).
There is therefore a need for robust surfactant mixtures comprising
alkyl ether sulfates, which, in oil production under the
abovementioned conditions, do not have at least some of the
abovementioned disadvantages and/or fulfil a maximum number of the
abovementioned properties or requirements.
GENERAL DESCRIPTION OF THE INVENTION
For the achievement of the above object, it has therefore been
found that, surprisingly, the demands are met at least partly by a
method for producing mineral oil from underground mineral oil
deposits (optionally by means of Winsor type III microemulsion
flooding), in which an aqueous saline surfactant formulation
comprising a surfactant mixture, for the purpose of lowering the
interfacial tension between oil and water to <0.1 mN/m,
preferably lowered to <0.05 mM/m, at deposit temperature, is
injected through at least one injection well into a mineral oil
deposit and crude oil is withdrawn through at least one production
well from the deposit, wherein the surfactant mixture comprises
at least one anionic surfactant (A) of the general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M (I) and at least one anionic surfactant (B) of the general
formula (II) R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M (II),
where a ratio of anionic surfactant (A) to anionic surfactant (B)
of 99:1 to 51:49 by weight is present in the surfactant mixture,
where R.sup.1 is a primary linear or branched, preferably linear,
saturated or unsaturated, aliphatic hydrocarbyl radical having 16
to 18 carbon atoms; R.sup.2 is a primary linear or branched,
preferably linear, saturated aliphatic hydrocarbyl radical having
12 to 17, preferably 12 to 14, carbon atoms; M is Na, K, NH.sub.4,
or NH(CH.sub.2CH.sub.2OH).sub.3; x is a number from 3 to 25; y is a
number from 0 to 20; and z is a number from 1 to 30;
where the sum total of x+y is a number from 3 to 35 and the x+y
alkoxylate groups may be arranged in random distribution, in
alternation or in blocks.
The aqueous saline surfactant formulation is understood to mean at
least the surfactant mixture which is dissolved in saline water
(for example during the injection operation). The saline water may,
inter alia, be river water, seawater, water from an aquifer close
to the deposit, so-called injection water, deposit water, so-called
production water which is being reinjected again, or mixtures of
the above-described waters. However, the saline water may also be
that which has been obtained from a more saline water: for example
partial desalination, depletion of the polyvalent cations or by
dilution with fresh water or drinking water. The surfactant mixture
can preferably be provided in a concentrate which, as a result of
the preparation, may also comprise salt. This is detailed further
in the paragraphs which follow.
Another aspect of the present invention is the surfactant mixture
as described herein. Accordingly, a surfactant mixture is claimed,
which comprises
at least one anionic surfactant (A) of the general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M (I) and at least one anionic surfactant (B) of the general
formula (II) R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M (II),
where a ratio of anionic surfactant (A) to anionic surfactant (B)
of 99:1 to 51:49 by weight is present in the surfactant mixture,
where R.sup.1 is a primary linear or branched, preferably linear,
saturated or unsaturated, aliphatic hydrocarbyl radical having 16
to 18 carbon atoms; R.sup.2 is a primary linear or branched,
preferably linear, saturated aliphatic hydrocarbyl radical having
12 to 17, preferably 12 to 14, carbon atoms; M is Na, K, NH.sub.4,
or NH(CH.sub.2CH.sub.2OH).sub.3; x is a number from 3 to 25; y is a
number from 0 to 20; and z is a number from 1 to 30; where the sum
total of x+y is a number from 3 to 35 and the x+y alkoxylate groups
may be arranged in random distribution, in alternation or in
blocks.
Further details are described in the following.
Accordingly, the present invention also relates to a method for
producing a surfactant mixture of anionic surfactant (A) of the
general formula (I) and anionic surfactant (B) of the general
formula (II) as described herein, wherein anionic surfactant (A)
and anionic surfactant (B) are made separately by alkoxylation of
alcohols R.sup.1OH and R.sup.2OH in a vessel followed by sulphation
with sulfur trioxide in a falling film reactor (including
neutralization step afterwards) and mixed finally.
A further aspect of the present invention relates to a concentrate
comprising the surfactant mixture as described herein and further
comprising at least water and/or a cosolvent. Accordingly the
concentrate comprises the surfactant mixture, which comprises at
least one surfactant (A) and at least one surfactant (B) as
described herein, and water or the concentrate comprises the
surfactant mixture, which comprises at least one surfactant (A) and
at least one surfactant (B) as described herein, and a cosolvent or
the concentrate comprises the surfactant mixture, which comprises
at least one surfactant (A) and at least one surfactant (B) as
described herein, and water as well as a cosolvent.
It is clear to a practitioner in the art that a cosolvent is
different from water as further described herein.
A further aspect of the present invention relates to the use of a
surfactant mixture as described herein or a concentrate of the
present invention in the production of mineral oil from underground
mineral oil deposits.
FURTHER DETAILS OF THE INVENTION
The present invention relates to a method for producing mineral oil
from underground mineral oil deposits (optionally by means of
Winsor type III microemulsion flooding), in which an aqueous saline
surfactant formulation comprising a surfactant mixture, for the
purpose of lowering the interfacial tension between oil and water
to <0.1 mN/m (preferably <0.05 mN/m) at deposit temperature,
is injected through at least one injection well into a mineral oil
deposit and crude oil is withdrawn through at least one production
well from the deposit, wherein the surfactant mixture comprises
at least one anionic surfactant (A) of the general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M (I) and at least one anionic surfactant (B) of the general
formula (II) R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M (II),
where a ratio of anionic surfactant (A) to anionic surfactant (B)
of 99:1 to 51:49 by weight is present in the surfactant mixture,
where R.sup.1 is a primary linear or branched, preferably linear,
saturated or unsaturated, aliphatic hydrocarbyl radical having 16
to 18 carbon atoms; and R.sup.2 is a primary linear or branched,
preferably linear, saturated aliphatic hydrocarbyl radical having
12 to 17, preferably 12 to 14, carbon atoms; M is Na, K, NH.sub.4,
or NH(CH.sub.2CH.sub.2OH).sub.3; x is a number from 3 to 25; y is a
number from 0 to 20; z is a number from 1 to 30; and where the sum
total of x+y is a number from 3 to 35 and the x+y alkoxylate groups
may be arranged in random distribution, in alternation or in
blocks.
In the above-defined general formulae, x, y and z are each natural
numbers including 0, i.e. 0, 1, 2 etc. However, it is clear to the
person skilled in the art in the field of polyalkoxylates that this
definition is the definition of a single surfactant in each case.
In the case of the presence of surfactant mixtures or surfactant
formulations comprising a plurality of surfactants of the general
formula, the numbers x, y and z are each mean values over all
molecules of the surfactants, since the alkoxylation of alcohol
with ethylene oxide or propylene oxide in each case affords a
certain distribution of chain lengths. This distribution can be
described in a manner known in principle by what is called the
polydispersity D. D=M.sub.w/M.sub.n is the ratio of the
weight-average molar mass and the number-average molar mass. The
polydispersity can be determined by methods known to those skilled
in the art, for example by means of gel permeation
chromatography.
The alkyleneoxy groups may be arranged in random distribution,
alternately or in blocks, i.e. in two, three, four or more
blocks.
Preferably, the x propyleneoxy and y ethyleneoxy groups are at
least partly arranged in blocks (in numerical terms, preferably to
an extent of at least 50%, more preferably to an extent of at least
60%, even more preferably to an extent of at least 70%, more
preferably to an extent of at least 80%, more preferably to an
extent of at least 90%, especially completely).
In the context of the present invention, "arranged in blocks" means
that at least one alkyleneoxy has a neighboring alkyleneoxy group
which is chemically identical, such that these at least two
alkyleneoxy units form a block.
More preferably, a sequence of blocks is arranged in that starting
from R.sup.1--O radical in formula (I) a propyleneoxy block with x
propyleneoxy groups follows and finally an ethyleneoxy block with y
ethyleneoxy groups.
The surfactant mixture comprises at least one anionic surfactant of
formula (I) and at least one anionic surfactant of formula (II).
However, the surfactant mixture typically comprises more than only
one anionic surfactant of formula (I) and more than one anionic
surfactant of formula (II) as explained above. The surfactant
mixture can also comprise further surfactant different from
surfactants (A) and (B). However, preferably the surfactant mixture
consists of at least one anionic surfactant of formula (I) and at
least one anionic surfactant of formula (II).
Preferably, the concentration of the surfactant mixture (all the
surfactants together) is 0.03% to 0.99% by weight, preferably 0.05%
to 0.49% by weight, based on the total amount of the aqueous saline
surfactant formulation.
Preferably, R.sup.1 is a primary linear, saturated or unsaturated,
aliphatic hydrocarbyl radical having 16 to 18 carbon atoms. More
preferably, R.sup.1 is a primary linear, saturated aliphatic
hydrocarbyl radical having 16 to 18 carbon atoms. Preferably,
R.sup.2 is a primary linear or branched saturated aliphatic
hydrocarbyl radical having 12 to 14 carbon atoms. More preferably,
R.sup.2 is a primary linear saturated aliphatic hydrocarbyl radical
having 12 to 14 carbon atoms. Preferably, M is Na. Preferably, x is
a number from 3 to 15. Preferably, y is a number from 0 to 10.
Preferably, z is a number from 1 to 5. Preferably, the sum total of
x+y is a number from 3 to 25.
Preferably, R.sup.1 is a primary linear, saturated, aliphatic
hydrocarbyl radical having 16 to 18 carbon atoms; R.sup.2 is a
primary linear saturated aliphatic hydrocarbyl radical having 12 to
14 carbon atoms; M is Na; x is a number from 3 to 15; y is a number
from 0 to 10; z is a number from 1 to 5; and the sum total of x+y
is a number from 3 to 25.
In a further particular embodiment of the invention, R.sup.1 is a
mixture of primary linear, saturated aliphatic hydrocarbyl radical
having 16 carbon atoms and of primary linear, saturated aliphatic
hydrocarbyl radical having 18 carbon atoms, wherein hydrocarbyl
radical having 16 carbon atoms to hydrocarbyl radical having 18
carbon atoms are preferably in a ratio of 20:80 to 40:60 on a molar
basis.
In the surfactant mixture, the ratio of anionic surfactant (A) to
anionic surfactant (B) is 99:1 to 51:49 by weight. As explained
above the ratio may vary during the oil recovery process. Thus, the
given ratio is to be understood as initial ratio, typically as
given on injection. This initial ratio is also given for the method
of producing the surfactant mixture and concentrates of the present
invention.
In a preferred embodiment, the ratio of anionic surfactant (A) to
anionic surfactant (B) is 95:5 to 55:45 by weight, more preferably
95:5 to 65:35 by weight, even more preferably of 95:5 to 75:25 by
weight.
The method for producing mineral oil from underground mineral oil
deposits (optionally by means of Winsor type III microemulsion
flooding), comprises the injection of an aqueous saline surfactant
formulation comprising a surfactant mixture, for the purpose of
lowering the interfacial tension between oil and water to <0.1
mN/m at deposit temperature. Preferably, the interfacial tension
between oil and water is lowered to <0.05 mN/m (even more
preferably <0.01 mN/m) at deposit temperature.
In a preferred embodiment, the aqueous saline surfactant
formulation comprises, in addition to the surfactant mixture, a
base, which is preferably selected from the group of alkali
hydroxides, such as sodium hydroxide or potassium hydroxide, or
from group of carbonates, such as sodium carbonate or sodium
bicarbonate, or from group of N-comprising compounds, such as
ammonia, ethanolamine, diethanolamine, triethanolamine, choline
hydroxide, or choline acetate. The term "base" also encompasses a
mixture of different bases, like two or more of the bases
mentioned.
In a further preferred embodiment, the aqueous saline surfactant
formulation further comprises a thickening polymer, preferably from
the group of the biopolymers or from the group of the copolymers
based on acrylamide. The copolymers based on acrylamide may
consist, for example, of the following units inter alia: acrylamide
and acrylic acid sodium salt, acrylamide and acrylic acid sodium
salt and AMPS (2-acrylamido-2-ethylpropanesulfonic acid sodium
salt).
In a further preferred embodiment, the underground mineral oil
deposit consists out of sandstone and deposit temperature is below
90.degree. C., preferably below 80.degree. C. and most preferably
below 70.degree. C.
In a further preferred embodiment, the mixture of anionic
surfactant (A) of the general formula (I) and anionic surfactant
(B) of the general formula (II) is provided in the form of a
concentrate comprising the surfactant mixture and at least water
and/or a cosolvent, preferably comprising 50% by weight to 90% by
weight of the surfactant mixture, 5% by weight to 30% by weight of
water and 5% by weight to 20% by weight of a cosolvent, based on
the total amount of the concentrate.
Accordingly in the method of producing mineral oil according to the
present invention a formulation is preferably used, wherein the
aqueous saline surfactant formulation is prepared from a
concentrate comprising the surfactant mixture of the present
invention and at least water and/or a cosolvent, preferably 50% by
weight to 90% by weight of the surfactant mixture, 5% by weight to
30% by weight of water and 5% by weight to 20% by weight of a
cosolvent, based on the total amount of the concentrate.
In this context, it is preferred that:
a) the cosolvent is selected from the group of the aliphatic
alcohols having 3 to 8 carbon atoms or from the group of the alkyl
monoethylene glycols, the alkyl diethylene glycols or the alkyl
triethylene glycols, where the alkyl radical is an aliphatic
hydrocarbyl radical having 3 to 6 carbon atoms;
and/or
b) the concentrate has a viscosity of <15000 mPas, preferably
<10000 mPas, more preferably <5000 mPas, most preferably
<3000 mPas at 50.degree. C. and at 10 s.sup.-1.
and/or
c) the amount of cosolvent by weight is equal or lower compared to
amount of water by weight in the concentrate.
Accordingly, the following preferences are given: a), b), c), a)
and b), a) and c), b) and c) as well as a), b) and c).
Advantage of such a concentration is that anionic surfactant (A) of
the general formula (I) and anionic surfactant (B) of the general
formula (II) are already mixed in the right stoichiometry and that
the operator in the oil field only has to dissolve the concentrate
in the injection water. Only one storage tank for the concentrate
is needed. Separate delivery of two surfactants each as concentrate
has the disadvantage that two storage tanks are needed and that
skilled workforce is required to survey the mixing in the right
ratio. The delivered concentrate comprising the desired mixture of
anionic surfactant (A) of the general formula (I) and anionic
surfactant (B) of the general formula (II) can be dosed out of the
storage tank into the injection water at ambient temperature (e.g.
20.degree. C.) or at elevated temperature (e.g. 60.degree. C.). For
example, in case of an alkali-surfactant-polymer flooding, the
injection water can already comprise the base, but it can be added
after the dissolving step of the surfactant. Afterwards, the
base-surfactant mixture dissolved in injection water is mixed with
polymer (pre-dissolved e.g. in injection water or in make-up
water). Finally, the base-surfactant-polymer mixture in injection
water can be pumped through an injection well into the mineral oil
deposit.
The anionic surfactant (A) of the general formula (I) and the
anionic surfactant (B) of the general formula (II) can be formed as
follows. First of all, it requires the preparation of a
corresponding alcohol which can be prepared as follows by way of
example: primary linear aliphatic alcohols are prepared by
hydrogenating fatty acids (prepared from natural vegetable or
animal fats and oils) or by hydrogenating fatty acid methyl esters.
Alternatively, primary linear aliphatic alcohols can be prepared by
the Ziegler process by oligomerizing ethylene over an aluminum
catalyst and then releasing the alcohol by adding water.
Subsequently, the primary alcohols R.sup.1OH or R.sup.2OH are
alkoxylated to give the corresponding prestages of anionic
surfactant (A) of the general formula (I) and the anionic
surfactant (B) of the general formula (II). The performance of such
alkoxylations is known in principle to those skilled in the art. It
is likewise known to those skilled in the art that the reaction
conditions, especially the selection of the catalyst, can influence
the molecular weight distribution of the alkoxylates.
The surfactants according to the general formulae can preferably be
prepared by base-catalyzed alkoxylation. In this case, the alcohol
R.sup.1OH or R.sup.2OH can be admixed in a pressure reactor with
alkali metal hydroxides (e.g. NaOH, KOH, CsOH), preferably
potassium hydroxide, or with alkali metal alkoxides, for example
sodium methoxide or potassium methoxide. Water (or MeOH) still
present in the mixture can be drawn off by means of reduced
pressure (for example <100 mbar) and/or increasing the
temperature (30 to 150.degree. C.). Thereafter, the alcohol is
present in the form of the corresponding alkoxide. This is followed
by inertization with inert gas (for example nitrogen) and stepwise
addition of the alkylene oxide(s) at temperatures of 60 to
180.degree. C. up to a pressure of not more than 20 bar (preferably
not more than 10 bar). In a preferred embodiment, the alkylene
oxide is metered in initially at 120.degree. C. In the course of
the reaction, the heat of reaction released causes the temperature
to rise up to 175.degree. C. However, the reaction temperature can
be kept between 120.degree. C. and 175.degree. C. by means of
cooling. In a further preferred embodiment of the invention, in
case of using R.sup.1OH the propylene oxide is added at a
temperature in the range from 120 to 170.degree. C., and
subsequently the ethylene oxide is added at a temperature in the
range from 120 to 170.degree. C. In a further preferred embodiment
of the invention, in case of using R.sup.2OH the ethylene oxide is
added at a temperature in the range from 120 to 170.degree. C. At
the end of the reaction, the catalyst can, for example, be
neutralized by adding acid (for example acetic acid or phosphoric
acid) and be filtered off if required. However, the material may
also remain unneutralized.
An alternative is the use of amines as catalyst for base-catalyzed
alkoxylation of R.sup.1OH or R.sup.2OH. For example, imidazole or
N,N-dimethylethanolamine can be used as catalyst. The alkoxylation
of the alcohols R.sup.1OH or R.sup.2OH can also be undertaken by
means of other methods, for example by acid-catalyzed alkoxylation.
In addition, it is possible to use, for example, double hydroxide
clays, as described in DE 4325237 A1, or it is possible to use
double metal cyanide catalysts (DMC catalysts). Suitable DMC
catalysts are disclosed, for example, in DE 10243361 A1, especially
in paragraphs [0029] to [0041] and the literature cited therein.
For example, it is possible to use catalysts of the Zn-Co type. To
perform the reaction, the alcohol R.sup.1OH or R.sup.2OH can be
admixed with the catalyst, and the mixture dewatered as described
above and reacted with the alkylene oxides as described. Typically,
not more than 1000 ppm of catalyst based on the mixture are used,
and the catalyst can remain in the product owing to this small
amount. The amount of catalyst may generally be less than 1000 ppm,
for example 250 ppm or less.
Finally, the anionic group--the sulfate group--is introduced. This
is known in principle to those skilled in the art. It is possible,
for example, to employ the reaction with sulfuric acid, sulfamic
acid or chlorosulfonic acid. Alternatively, use of sulfur trioxide
in a falling-film reactor with subsequent neutralization is
possible. Latter route is the preferred as it is the most
economical process. Gaseous sulfur trioxide mixed with e.g.
nitrogen (1 to 9 volume percent of sulfur trioxide in the mixture)
is reacted with the alkyl alkoxylate
(R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--H
or R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--H) in a falling film
reactor (preferably in a falling film reactor from company
Ballestra). The liquid alkyl alkoxylate runs as thin film down the
wall of the falling film reactor. The gaseous sulfur trioxide mixed
with gas (e.g. nitrogen) flows through the tube too and reacts with
the alkyl alkoxylate. Reaction temperature is kept between 15 and
90.degree. C. (preferably between 20 and 80.degree. C.) into
reaction. The obtained semi sulfuric acid ester is neutralized
using sodium hydroxide, potassium hydroxide, ammonia in water or
triethanolamine in water. In addition, a cosolvent can be added
during the neutralization step in order to break gel phases
(purpose to lower viscosity) and to avoid an incomplete
neutralization.
The invention relates to manufacturing processes of the surfactant
mixture, comprising anionic surfactant (A) of the general formula
(I) and anionic surfactant (B) of the general formula (II).
According to the present invention, the anionic surfactant (A) and
anionic surfactant (B) are made separately by alkoxylation of
alcohols R.sup.1OH and R.sup.2OH in a vessel followed by sulphation
with sulfur trioxide in a falling film reactor (including
neutralization step afterwards) and mixed finally.
The present invention also relates to a concentrate comprising the
surfactant mixture described herein and furtehr comrising water
and/or a cosolvent.
Accordingly the concentrate comprises the surfactant mixture with a
ratio of anionic surfactant (A) to anionic surfactant (B) of 55:45
to 95:5 by weight, preferably 65:35 to 95:5 by weight, most
preferably of 75:25 to 95:5 by weight.
Accordingly, the concentrate comprising the surfactant mixture
preferably comprises 50% by weight to 90% by weight of the
surfactant mixture, 5% by weight to 30% by weight of water and 5%
by weight to 20% by weight of a cosolvent, based on the total
amount of the concentrate, where preferably a) the cosolvent is
selected from the group of the aliphatic alcohols having 3 to 8
carbon atoms or from the group of the alkyl monoethylene glycols,
the alkyl diethylene glycols or the alkyl triethylene glycols,
where the alkyl radical is an aliphatic hydrocarbyl radical having
3 to 6 carbon atoms; and/or b) the concentrate has a viscosity of
<15000 mPas, preferably <10000 mPas, more preferably <5000
mPas, most preferably <3000 mPas at 50.degree. C. and at 10
s.sup.-1. and/or c) amount of cosolvent by weight is equal or lower
compared to amount of water by weight in the concentrate.
Accordingly, the following preferences are given: a), b), c), a)
and b), a) and c), b) and c) as well as a), b) and c).
The concentrate preferably comprises at least one organic
cosolvent. These are preferably completely water-miscible solvents,
but it is also possible to use solvents having only partial water
miscibility. In general, the solubility should be at least 50 g/l,
preferably at least 100 g/I. Examples include aliphatic C.sub.4 to
C.sub.8 alcohols, preferably C.sub.4 to C.sub.6 alcohols, which may
be substituted by 1 to 5, preferably 1 to 3, ethyleneoxy units to
achieve sufficient water solubility. Further examples include
aliphatic diols having 2 to 8 carbon atoms, which may optionally
also have further substitution. For example, the cosolvent may be
at least one selected from the group of 2-butanol, 2
methyl-1-propanol, butylglycol, butyldiglycol and
butyltriglycol.
The surfactant mixture as described herein and the concentrate of
the present invention can be used in the production of mineral oil
from underground mineral oil deposit.
According to a further aspect of the present invention in the
method of mineral oil production according to the present invention
a polymer or a foam for mobility control can be added. The polymer
can optionally be injected into the deposit together with the
surfactant formulation, followed by the surfactant formulation. It
can also be injected only with the surfactant formulation or only
after surfactant formulation. The polymers may be copolymers based
on acrylamide or a biopolymer. The copolymer may consist, for
example, of the following units inter alia: acrylamide and acrylic
acid sodium salt acrylamide and acrylic acid sodium salt and
N-vinylpyrrolidone acrylamide and acrylic acid sodium salt and AMPS
(2-acrylamido-2-methylpropanesulfonic acid sodium salt) acrylamide
and acrylic acid sodium salt and AMPS
(2-acrylamido-2-methylpropanesulfonic acid sodium salt) and
N-vinylpyrrolidone.
The copolymer may also additionally comprise associative groups.
Usable copolymers are described in EP 2432807 or in WO 2014095621.
Further usable copolymers are described in U.S. Pat. No.
7,700,702.
The polymers can be stabilized by addition of further additives
such as biocides, stabilizers, free radical scavengers and
inhibitors.
The foam can be produced at the deposit surface or in situ in the
deposit by injection of gases such as nitrogen or gaseous
hydrocarbons such as methane, ethane or propane. The foam can be
produced and stabilized by adding the surfactant mixture claimed or
else further surfactants.
Optionally, it is also possible to add a base such as alkali metal
hydroxide or alkali metal carbonate to the surfactant formulation,
in which case the addition is optionally combined with the addition
of complexing agents or polyacrylates in order to prevent
precipitation as a result of the presence of polyvalent cations. In
addition, it is also possible to add a cosolvent to the
formulation.
This gives rise to the following (combined) methods: surfactant
flooding Winsor type III microemulsion flooding surfactant/polymer
flooding Winsor type III microemulsion/polymer flooding
alkali/surfactant/polymer flooding alkali/Winsor type III
microemulsion/polymer flooding surfactant/foam flooding Winsor type
III microemulsion/foam flooding alkali/surfactant/foam flooding
alkali/Winsor type III microemulsion/foam flooding
In a preferred embodiment of the invention, one of the first four
methods is employed (surfactant flooding, Winsor type III
microemulsion flooding, surfactant/polymer flooding or Winsor type
III microemulsion/polymer flooding). Particular preference is given
to Winsor type III microemulsion/polymer flooding.
In Winsor type III microemulsion/polymer flooding, in the first
step, a surfactant formulation is injected with or without polymer.
The surfactant formulation, on contact with crude oil, results in
the formation of a Winsor type III microemulsion. In the second
step, only polymer is injected. In the first step in each case, it
is possible to use aqueous formulations having higher salinity than
in the second step. Alternatively, both steps can also be conducted
with water of equal salinity.
In one embodiment, the methods can of course also be combined with
water flooding. In the case of water flooding, water is injected
into a mineral oil deposit through at least one injection well, and
crude oil is withdrawn from the deposit through at least one
production well. The water may be freshwater or saline water such
as seawater or deposit water. After the water flooding, the method
of the invention may be employed.
To execute the method of the invention, at least one production
well and at least one injection well are sunk into the mineral oil
deposit. In general, a deposit is provided with several injection
wells and with several production wells. The wells can be vertical
and/or horizontal. An aqueous formulation of the water-soluble
components described is injected through the at least one injection
well into the mineral oil deposit, and crude oil is withdrawn from
the deposit through at least one production well. As a result of
the pressure generated by the aqueous formulation injected, called
the "flood", the mineral oil flows in the direction of the
production well and is produced via the production well. The term
"mineral oil" in this context of course does not just mean
single-phase oil; instead, the term also encompasses the usual
crude oil-water emulsions. It will be clear to the person skilled
in the art that a mineral oil deposit may also have a certain
temperature distribution. Said deposit temperature is based on the
region of the deposit between the injection and production wells
which is covered by the flooding with aqueous solutions. Methods of
determining the temperature distribution of a mineral oil deposit
are known in principle to those skilled in the art. The temperature
distribution is generally determined from temperature measurements
at particular sites in the formation in combination with simulation
calculations; the simulation calculations also take account of the
amounts of heat introduced into the formation and the amounts of
heat removed from the formation.
The method of the invention can especially be employed in mineral
oil deposits having an average porosity of 5 mD to 4 D, preferably
50 mD to 2 D and more preferably 200 mD to 1 D. The permeability of
a mineral oil formation is reported by the person skilled in the
art in the unit "darcy" (abbreviated to "D" or "mD" for
"millidarcies"), and can be determined from the flow rate of a
liquid phase in the mineral oil formation as a function of the
pressure differential applied. The flow rate can be determined in
core flooding tests with drill cores taken from the formation.
Details of this can be found, for example, in K. Weggen, G. Pusch,
H. Rischmuller in "Oil and Gas", pages 37 ff., Ullmann's
Encyclopedia of Industrial Chemistry, Online Edition, Wiley-VCH,
Weinheim 2010. It will be clear to the person skilled in the art
that the permeability in a mineral oil deposit need not be
homogeneous, but generally has a certain distribution, and the
permeability reported for a mineral oil deposit is accordingly an
average permeability.
To execute the method for oil production, an aqueous formulation is
used, comprising, as well as water, at least the described
surfactant mixture of anionic surfactant (A) of the general formula
(I) and the anionic surfactant (B) of the general formula (II).
Optionally, the formulation may additionally comprise further
surfactants. These are, for example, anionic surfactants of the
alkylarylsulfonate or olefinsulfonate (alpha-olefinsulfonate or
internal olefinsulfonate) type and/or nonionic surfactants of the
alkyl ethoxylate or alkyl polyglucoside type. These further
surfactants may especially also be oligomeric or polymeric
surfactants. It is advantageous to use such polymeric
co-surfactants to reduce the amounts of surfactants needed to form
a microemulsion. Such polymeric co surfactants are therefore also
referred to as "microemulsion boosters". Examples of such polymeric
surfactants comprise amphiphilic block copolymers which comprise at
least one hydrophilic block and at least one hydrophobic block.
Examples comprise polypropylene oxide-polyethylene oxide block
copolymers, polyisobutene-polyethylene oxide block copolymers, and
comb polymers with polyethylene oxide side chains and a hydrophobic
main chain, where the main chain preferably comprises essentially
olefins or (meth)acrylates as monomers. The term "polyethylene
oxide" here should in each case include polyethylene oxide blocks
comprising propylene oxide units as defined above. Further details
of such surfactants are disclosed in WO 2006/131541 A1.
The formulation is made up in water comprising salts. Of course,
there may also be mixtures of different salts. For example, it is
possible to use seawater to make up the aqueous formulation, or it
is possible to use produced formation water, which is reused in
this way. In the case of offshore production platforms, the
formulation is generally made up in seawater. In the case of
onshore production facilities, the polymer can advantageously first
be dissolved in fresh water and the solution obtained can be
diluted to the desired use concentration with formation water.
Alternatively, the salt content of the injection water can be
reduced by means of desalination techniques (e.g. use of membranes
for ultrafiltration, nanofiltration, reverse osmosis, and forward
osmosis or e.g. precipitation of bivalent cations with bivalent
anions).
The salts may especially be alkali metal salts and alkaline earth
metal salts. Examples of typical anions include Na.sup.+, K.sup.+,
Mg.sup.2+ and/or Ca.sup.2+, and examples of typical cations include
chloride, bromide, hydrogencarbonate, sulfate or borate. In case,
that injection water is softened, then no alkaline earth metal ions
are present.
In general, at least one or more than one alkali metal ion is
present, especially at least Na.sup.+. In addition, alkaline earth
metal ions are also maybe present, in which case the weight ratio
of alkali metal ions / alkaline earth metal ions is generally
.gtoreq.2, preferably 3. In case, that injection water is softened,
then no alkaline earth metal ions are present. Anions present are
generally at least one or more than one halide ion(s), especially
at least Cl.sup.-. In general, the amount of Cl.sup.- is at least
50% by weight, preferably at least 65% by weight, based on the sum
total of all the anions.
The total amount of all the salts in the aqueous formulation may be
up to 350 000 ppm (parts by weight), based on the sum total of all
the components in the formulation, for example 500 ppm to 350 000
ppm, especially 2000 ppm to 250 000 ppm. If seawater is used to
make up the formulation, the salt content may be 2000 ppm to 40 000
ppm, and, if formation water is used, the salt content may be 2000
ppm to 250 000 ppm, for example 3000 ppm to 100 000 ppm. The amount
of alkaline earth metal ions may preferably be 0 to 53 000 ppm,
more preferably 0 ppm to 20 000 ppm and even more preferably 0 to
6000 ppm.
Additives can be used, for example, in order to prevent unwanted
side effects, for example the unwanted precipitation of salts, or
in order to stabilize the polymer used. The polymer-containing
formulations injected into the formation in the flooding process
flow only very gradually in the direction of the production well,
meaning that they remain under formation conditions in the
formation for a prolonged period. Degradation of the polymer
results in a decrease in the viscosity. This either has to be taken
into account through the use of a higher amount of polymer, or else
it has to be accepted that the efficiency of the method will
worsen. In each case, the economic viability of the method worsens.
A multitude of mechanisms may be responsible for the degradation of
the polymer. By means of suitable additives, the polymer
degradation can be prevented or at least delayed according to the
conditions.
In one embodiment of the invention, the aqueous formulation used
comprises at least one oxygen scavenger. Oxygen scavengers react
with oxygen which may possibly be present in the aqueous
formulation and thus prevent the oxygen from being able to attack
the polymer or polyether groups. Examples of oxygen scavengers
comprise sulfites, for example Na.sub.2SO.sub.3, bisulfites,
phosphites, hypophosphites or dithionites.
In a further embodiment of the invention, the aqueous formulation
used comprises at least one free radical scavenger. Free radical
scavengers can be used to counteract the degradation of the polymer
by free radicals. Compounds of this kind can form stable compounds
with free radicals. Free radical scavengers are known in principle
to those skilled in the art. For example, they may be stabilizers
selected from the group of sulfur compounds, secondary amines,
sterically hindered amines, N-oxides, nitroso compounds, aromatic
hydroxyl compounds or ketones. Examples of sulfur compounds include
thiourea, substituted thioureas such as N,N'-dimethylthiourea,
N,N'-diethylthiourea, N,N'-diphenylthiourea, thiocyanates, for
example ammonium thiocyanate or potassium thiocyanate,
tetramethylthiuram disulfide, and mercaptans such as
2-mercaptobenzothiazole or 2-mercaptobenzimidazole or salts
thereof, for example the sodium salts, sodium
dimethyldithiocarbamate, 2,2'-dithiobis(benzothiazole),
4,4'-thiobis(6-t-butyl-m-cresol). Further examples include
phenoxazine, salts of carboxylated phenoxazine, carboxylated
phenoxazine, methylene blue, dicyandiamide, guanidine, cyanamide,
paramethoxyphenol, sodium salt of paramethoxyphenol,
2-methylhydroquinone, salts of 2-methylhydroquinone,
2,6-di-t-butyl-4-methylphenol, butylhydroxyanisole,
8-hydroxyquinoline, 2,5-di(t-amyl)-hydroquinone,
5-hydroxy-1,4-naphthoquinone, 2,5-di(t-amyl)hydroquinone, dimedone,
propyl 3,4,5-trihydroxybenzoate, ammonium
N-nitrosophenylhydroxylamine,
4-hydroxy-2,2,6,6-tetramethyloxypiperidine,
N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and
1,2,2,6,6-pentamethyl-4-piperidinol. Preference is given to
sterically hindered amines such as
1,2,2,6,6-pentamethyl-4-piperidinol and sulfur compounds, mercapto
compounds, especially 2-mercaptobenzothiazole or
2-mercaptobenzimidazole or salts thereof, for example the sodium
salts, and particular preference is given to
2-mercaptobenzothiazole or salts thereof.
In a further embodiment of the invention, the aqueous formulation
used comprises at least one sacrificial reagent. Sacrificial
reagents can react with free radicals and thus render them
harmless. Examples include especially alcohols. Alcohols can be
oxidized by free radicals, for example to ketones. Examples include
monoalcohols and polyalcohols, for example 1-propanol, 2-propanol,
propylene glycol, glycerol, butanediol or pentaerythritol.
In a further embodiment of the invention, the aqueous formulation
used comprises at least one complexing agent. It is of course
possible to use mixtures of various complexing agents. Complexing
agents are generally anionic compounds which can complex especially
divalent and higher-valency metal ions, for example Mg.sup.+ or
Ca.sup.2 +. In this way, it is possible, for example, to prevent
any unwanted precipitation. In addition, it is possible to prevent
any polyvalent metal ions present from crosslinking the polymer by
means of acidic groups present, especially COOH group. The
complexing agents may especially be carboxylic acid or phosphonic
acid derivatives. Examples of complexing agents include
ethylenediaminetetraacetic acid (EDTA), ethylenediaminesuccinic
acid (EDDS), diethylenetriaminepentamethylenephosphonic acid
(DTPMP), methylglycinediacetic acid (MGDA) and nitrilotriacetic
acid (NTA). Of course, the corresponding salts of each may also be
involved, for example the corresponding sodium salts. In a
particularly preferred embodiment of the invention, MGDA is used as
complexing agent
As an alternative to or in addition to the abovementioned chelating
agents, it is also possible to use polyacrylates.
In a further embodiment of the invention, the formulation comprises
at least one organic cosolvent. These are preferably completely
water-miscible solvents, but it is also possible to use solvents
having only partial water miscibility. In general, the solubility
should be at least 50 g/l, preferably at least 100 g/l. Examples
include aliphatic C.sub.4 to C.sub.b 8 alcohols, preferably C.sub.4
to C.sub.6 alcohols, which may be substituted by 1 to 5, preferably
1 to 3, ethyleneoxy units to achieve sufficient water solubility.
Further examples include aliphatic diols having 2 to 8 carbon
atoms, which may optionally also have further substitution. For
example, the cosolvent may be at least one selected from the group
of 2-butanol, 2 methyl-1-propanol, butylglycol, butyldiglycol and
butyltriglycol.
The concentration of the polymer in the aqueous formulation is
fixed such that the aqueous formulation has the desired viscosity
for the end use. The viscosity of the formulation should generally
be at least 5 mPas (measured at 25.degree. C. and a shear rate of 7
s.sup.-1), preferably at least 10 mPas.
According to the invention, the concentration of the polymer in the
formulation is 0.02% to 2% by weight, based on the sum total of all
the components of the aqueous formulation. The amount is preferably
0.05% to 0.5% by weight, more preferably 0.1% to 0.3% by weight
and, for example, 0.1% to 0.2% by weight.
The aqueous polymer-comprising formulation can be prepared by
initially charging the water, sprinkling the polymer in as a powder
and mixing it with the water. Apparatus for dissolving polymers and
injecting the aqueous solutions into underground formations is
known in principle to those skilled in the art.
The injecting of the aqueous formulation can be undertaken by means
of customary apparatuses. The formulation can be injected into one
or more injection wells by means of customary pumps. The injection
wells are typically lined with steel tubes cemented in place, and
the steel tubes are perforated at the desired point. The
formulation enters the mineral oil formation from the injection
well through the perforation. The pressure applied by means of the
pumps, in a manner known in principle, is used to fix the flow rate
of the formulation and hence also the shear stress with which the
aqueous formulation enters the formation. The shear stress on entry
into the formation can be calculated by the person skilled in the
art in a manner known in principle on the basis of the
Hagen-Poiseuille law, using the area through which the flow passes
on entry into the formation, the mean pore radius and the volume
flow rate. The average permeability of the formation can be found
as described in a manner known in principle. Naturally, the greater
the volume flow rate of aqueous polymer formulation injected into
the formation, the greater the shear stress.
The rate of injection can be fixed by the person skilled in the art
according to the conditions in the formation. Preferably, the shear
rate on entry of the aqueous polymer formulation into the formation
is at least 30 000 s.sup.-1, preferably at least 60 000 s.sup.-1
and more preferably at least 90 000 s.sup.-1.
In one embodiment of the invention, the method of the invention is
a flooding method in which a base and typically a complexing agent
or a polyacrylate is used. This is typically the case when the
proportion of polyvalent cations in the deposit water is low
(100-400 ppm). An exception is sodium metaborate, which can be used
as a base in the presence of significant amounts of polyvalent
cations even without complexing agent.
The pH of the aqueous formulation is generally at least 8,
preferably at least 9, especially 9 to 13, preferably 10 to 12 and,
for example, 10.5 to 11.
In principle, it is possible to use any kind of base with which the
desired pH can be attained, and the person skilled in the art will
make a suitable selection. Examples of suitable bases include
alkali metal hydroxides, for example NaOH or KOH, or alkali metal
carbonates, for example Na.sub.2CO.sub.3. In addition, the bases
may be basic salts, for example alkali metal salts of carboxylic
acids, phosphoric acid, or especially complexing agents comprising
acidic groups in the base form, such as EDTANa.sub.4.
Mineral oil typically also comprises various carboxylic acids, for
example naphthenic acids, which are converted to the corresponding
salts by the basic formulation. The salts act as naturally
occurring surfactants and thus support the process of oil
removal.
With complexing agents, it is advantageously possible to prevent
unwanted precipitation of sparingly soluble salts, especially Ca
and Mg salts, when the alkaline aqueous formulation comes into
contact with the corresponding metal ions and/or aqueous
formulations for the process comprising corresponding salts are
used. The amounts of complexing agents are selected by the person
skilled in the art. It may, for example, be 0.1% to 4% by weight,
based on the sum total of all the components of the aqueous
formulation.
In a particularly preferred embodiment of the invention, however, a
method of mineral oil production is employed in which a base (e.g.
alkali metal hydroxides or alkali metal carbonates) is used.
The following examples are intended to illustrate the invention and
its advantages in detail:
Preparation of the Mixture Comprising Anionic Surfactant (A) and
Anionic Surfactant (B):
Abbreviations used: EO ethyleneoxy PO propyleneoxy BuO
1,2-butyleneoxy For the synthesis, the following alcohols were
used:
TABLE-US-00001 Alcohol Description C.sub.16C.sub.18 Commercially
available tallow fatty alcohol mixture consisting of linear
saturated primary C.sub.16H.sub.33--OH and C.sub.18H.sub.37--OH
C.sub.12C.sub.14 Commercially available fatty alcohol mixture
consisting of linear saturated primary C.sub.12H.sub.25--OH and
C.sub.14H.sub.29--OH
1 a) C16C18-7 PO-H
Corresponds to prestage (intermediate) of surfactant (A) of the
general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--H
with R.sup.1=C.sub.16H.sub.33/C.sub.18H.sub.37, x=7 and y=0
A 2 L pressure autoclave with anchor stirrer was initially charged
with 384 g (1.5 mol, 1.0 eq) of C16C18 alcohol and the stirrer was
switched on. Thereafter, 5.2 g of 50% aqueous KOH solution (0.046
mol of KOH, 2.6 g of KOH) were added, a reduced pressure of 25 mbar
was applied, and the mixture was heated to 100.degree. C. and kept
there for 120 min, in order to distill off the water. The mixture
was purged three times with N.sub.2. Thereafter, the vessel was
tested for pressure retention, 1.0 bar gauge (2.0 bar absolute) was
set, the mixture was heated to 130.degree. C. and then the pressure
was set to 2.0 bar absolute. At 150 revolutions per minute, 609 g
(10.5 mol, 7.0 eq) of propylene oxide were metered in at
130.degree. C. within 7 h; pmax was 4.0 bar absolute. The mixture
was stirred at 130.degree. C. for a further 2 h. The pressure was
constant, cooled down to 100.degree. C. and decompressed to 1.0 bar
absolute. A vacuum of <10 mbar was applied and residual oxide
was drawn off for 2 h. The vacuum was broken with N.sub.2 and the
product was decanted at 80.degree. C. under N.sub.2. In a rotary
evaporator, the mixture was stirred at 100.degree. C. and <10
mbar for 3 h. Then it was filled into a flask with stirrer and 2.76
g (0.046 mol) of acetic acid was added. Analysis (mass spectrum,
GPC, 1H NMR in CDCl3, 1H NMR in MeOD) confirmed the mean
composition C16C18-7 PO-H.
2 a) C12C14-2 EO-H
Corresponds to prestage of surfactant (B) of the general formula
(II) R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--H with
R.sup.1=C.sub.12H.sub.25/C.sub.14H.sub.29, and z=2
A 2 L pressure autoclave with anchor stirrer was initially charged
with 290 g (3.0 mol, 1.0 eq) of C12C14 alcohol and the stirrer was
switched on. Thereafter, 10.4 g of 50% aqueous KOH solution (0.092
mol of KOH, 5.2 g of KOH) were added, a reduced pressure of 35 mbar
was applied, and the mixture was heated to 100.degree. C. and kept
there for 120 min, in order to distill off the water. The mixture
was purged three times with N.sub.2. Thereafter, the vessel was
tested for pressure retention, 1.0 bar gauge (2.0 bar absolute) was
set, the mixture was heated to 130.degree. C. and then the pressure
was set to 2.0 bar absolute. At 150 revolutions per minute, 264 g
(6 mol, 2.0 eq) of ethylene oxide were metered in at 130.degree. C.
within 3 h; pmax was 4.0 bar absolute. The mixture was stirred at
130.degree. C. for a further 2 h. The pressure was constant, cooled
down to 100.degree. C. and decompressed to 1.0 bar absolute. A
vacuum of 35 mbar was applied and residual oxide was drawn off for
2 h. The vacuum was broken with N.sub.2 and the product was
decanted at 80.degree. C. under N.sub.2. In a rotary evaporator,
the mixture was stirred at 100.degree. C. and 35 mbar for 3 h. Then
it was filled into a flask with stirrer and 5.52 g (0.092 mol) of
acetic acid was added. Analysis (mass spectrum, GPC, 1H NMR in
CDCl3, 1H NMR in MeOD) confirmed the mean composition C12C14 -2
EO-H.
1 b) C16C18 -7 PO-SO.sub.4Na
Corresponds to surfactant (A) of the general formula (II)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M with R.sup.1=C.sub.16H.sub.33/C.sub.18H.sub.37, x=7, y=0,
and M=Na
In an one liter round-bottom flask with anchor stirrer, C16C18-7
PO-H (166.9 g, 0.25 mol, 1.0 eq) was dissolved under stirring in
dichloromethane (330 g) and cooled to 5 to 10.degree. C.
Thereafter, chloro sulfonic acid (37.7 g, 0.325 mol, 1.3 eq) was
added dropwise such that the temperature did not exceed 10.degree.
C. The mixture was allowed to warm up to 21.degree. C. and was
stirred under a nitrogen stream at this temperature for 4 h before
the above reaction mixture was added dropwise into a two liter
round-bottom-flask with anchor stirrer, which comprised a stirred
solution of NaOH (0.3375 mol NaOH, 13.5 g NaOH, 1.35 eq) in water
(400 g) at max. 15.degree. C. The resulting pH to 8 to 9 was
adjusted by addition HCl in water. The dichloromethane was removed
at 50.degree. C. and at 30 mbar using a rotary evaporator. The
water content was determined (Karl-Fischer method), butyl
diethylene glycol (48 g) was added and then the water was further
at 50.degree. C. and at 30 mbar using a rotary evaporator until a
water content of 28 wt % was achieved. The solution comprised 57 wt
% surfactants, 14 wt % cosolvent, 28 wt % water and less than 1 wt
% salt. The product was characterized by .sup.1H NMR and confirmed
the desired structure. Sulfation degree was significantly above 90
mol %.
2 b) C12C14-2 EO-SO.sub.4Na
Corresponds to surfactant (B) of the general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with
R.sup.1=C.sub.12H.sub.25/C.sub.14H.sub.29, z=2, and M=Na.
In an one liter round-bottom flask with anchor stirrer, C12C14 -2
EO-H (140.5 g, 0.50 mol, 1.0 eq) was dissolved under stirring in
dichloromethane (280 g) and cooled to 5 to 10.degree. C.
Thereafter, chloro sulfonic acid (75.4 g, 0.65 mol, 1.3 eq) was
added dropwise such that the temperature did not exceed 10.degree.
C. The mixture was allowed to warm up to 21.degree. C. and was
stirred under a nitrogen stream at this temperature for 4 h before
the above reaction mixture was added dropwise into a two liter
round-bottom-flask with anchor stirrer, which comprised a stirred
solution of NaOH (0.675 mol NaOH, 27 g NaOH, 1.35 eq) in water (300
g) at max. 15.degree. C. The resulting pH to 8 to 9 was adjusted by
addition HCl in water. The dichloromethane was removed at
50.degree. C. and at 30 mbar using a rotary evaporator. The water
content was determined (Karl-Fischer method) and then the water was
further at 50.degree. C. and at 30 mbar using a rotary evaporator
until a water content of 30 wt % was achieved. The solution
comprised 69 wt % surfactants, 30 wt % water and less than 1 wt %
salt. The product was characterized by .sup.1H NMR and confirmed
the desired structure. Sulfation degree was significantly above 90
mol %.
3a) Concentrate of ca. 9:1 mixture of C16C18 -7 PO-SO.sub.4Na to
C12C14-2 EO-SO4Na Corresponds to mixture of surfactant (A) of the
general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2).sub.y---
SO.sub.3M with R.sup.1=C.sub.16H.sub.33/C.sub.18H.sub.37, x=7, y=0,
and M=Na with surfactant (B) of the general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--H with
R.sup.1=C.sub.12H.sub.25/C.sub.14H.sub.29, z=2, and M=Na in the
ratio of 89:11 by weight.
In a 100 ml round bottom flask with stirrer bar, 15 g of surfactant
solution of C16C18-7 PO-SO4Na from example 2 a), comprising 57 wt %
surfactants, 14 wt % butyl diethylene glycole, 28 wt % water and
less than 1 wt % salt, were added and heated to 50.degree. C. under
stirring. Then, 1.38 g of surfactant solution of C12C14-2 EO-SO4Na
from example 2 b), comprising 69 wt % surfactants, 30 wt % water
and less than 1 wt % salt, were added. Mixture was stirred for 1 h
at 50.degree. C. and then cooled to 20.degree. C. The obtained
concentrate comprised a ca. 9:1 ratio (by weight) of C16C18-7
PO-SO4Na to C12C14-2EO-SO4Na. Total surfactant content in the
concentrate was ca. 58% by weight, content of cosolvent butyl
diethylene glycole was ca. 13% by weight, content of water was ca.
28% by weight, and salt content was less than 1% by weight.
3 b) Concentrate of ca. 6:4 mixture of C16C18-7 PO-SO.sub.4Na to
C12C14-2 EO-SO4Na Corresponds to mixture of surfactant (A) of the
general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--
-SO.sub.3M with R.sup.1=C.sub.16H.sub.33/C.sub.18H.sub.37, x=7,
y=0, and M=Na with surfactant (B) of the general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--H with
R.sup.1=C.sub.12H.sub.25/C.sub.14H.sub.29, z=2, and M=Na in the
ratio of 60:40 by weight.
In a 100 ml round bottom flask with stirrer bar, 9 g of surfactant
solution of C16C18-7PO-SO4Na from example 2 a), comprising 57 wt %
surfactants, 14 wt % butyl diethylene glycole, 28 wt % water and
less than 1 wt % salt, were added and heated to 50.degree. C. under
stirring. Then, 5 g of surfactant solution of C12C14 -2 EO-SO4Na
from example 2 b), comprising 69 wt % surfactants, 30 wt % water
and less than 1 wt % salt, were added. Mixture was stirred for 1 h
at 50.degree. C. and then cooled to 20.degree. C. The obtained
concentrate comprised a ca. 6:4 ratio (by weight) of C16C18-7
PO-SO4Na to C12C14-2 EO-SO4Na. Total surfactant content in the
concentrate was ca. 61% by weight, content of cosolvent butyl
diethylene glycole was ca. 9% by weight, content of water was ca.
29% by weight, and salt content was less than 1% by weight.
Further surfactants and concentrates are prepared in an analogous
way. For example, an aqueous cosolvent-free concentrate of C16C18-7
PO-SO.sub.4Na was made according to procedure above but without
addition of cosolvent butyl diethylene glycole. In order to cope
with gel formation at 20.degree. C. during synthesis, a lower
concentration (30 wt % and lower) of alkyl ether sulfates can be
targeted. If higher concentrations are needed, then water can be
removed under reduced pressure at 50.degree. C. in a rotary
evaporator.
Testing of the mixture comprising anionic surfactant (A) and
anionic surfactant (B):
Test methods:
Determination of stability
The stability of the concentrates of the anionic surfactant
(A)/anionic surfactant (B) mixture was determined by visual
assessment after storage at appropriate temperatures for 12 weeks
at 20.degree. C. The concentrates comprised water and butyl
diethylene glycol, and also the anionic surfactant (A)/anionic
surfactant (B) mixture described in the preparation examples.
Notice was taken as to whether the concentrates remain homogeneous
or whether significant phase separations which prevent homogeneous
sampling arise. In addition, the concentrates (where possible) were
heated to 50.degree. C. and cooled again at 20.degree. C., and an
observation was made as to whether an irreversible phase separation
arises.
Determination of viscosity
The dynamic viscosities of the concentrates of the anionic
surfactant (A)/anionic surfactant (B) mixture were determined with
an Anton Parr MCR302 viscometer. The concentrates comprised water
and butyl diethylene glycol (BDG), and also anionic surfactant
(A)/anionic surfactant (B) mixture described in the preparation
examples. The viscosities were conducted at shear rates of 10, 20,
and (optionally) 100 s.sup.-1 and temperatures of 20 and 50.degree.
C.
Determination of solubility
The surfactants in the concentration to be examined in each case in
saline water with the particular salt composition were stirred at
20-30.degree. C. for 30 min. Thereafter, the mixture was heated
stepwise until turbidity or a phase separation set in. This was
followed by cautious cooling, and the point at which the solution
became clear or scattering became slight again was noted. This was
recorded as the cloud point.
At particular fixed temperatures, the appearance of the surfactant
solution in saline water was noted. Clear solutions or solutions
which have slight scatter and become somewhat lighter in color
again through gentle shear (but do not foam with time) are regarded
as acceptable. Said slightly scattering surfactant solutions were
filtered through a filter having pore size 2 .mu.m. No removal at
all was found.
Determination of interfacial tension
Interfacial tensions of crude oil with respect to saline water were
determined in the presence of the surfactant solution at a
temperature by the spinning drop method on an SVT20 from
DataPhysics. For this purpose, an oil droplet was injected into a
capillary filled with saline surfactant solution at temperature and
the expansion of the droplet at approximately 4500 revolutions per
minute was observed and the evolution of the interfacial tension
with time was noted. The interfacial tension IFT (or s .sub.II) is
calculated--as described by Hans-Dieter Dorfler in "Grenzflachen
und kolloid-disperse Systeme" [Interfaces and Colloidally Disperse
Systems], Springer Verlag Berlin Heidelberg 2002--by the following
formula from the cylinder diameter d.sub.z, the speed of rotation
w, and the density differential:
(d.sub.1-d.sub.2):s.sub.II=0.25d.sub.z.sup.3w2(d.sub.1-d.sub.2).
The API gravity (American Petroleum Institute gravity) is a
conventional unit of density commonly used in the USA for crude
oils. It is used globally for characterization and as a quality
standard for crude oil. The API gravity is calculated from the
relative density p.sub.rel of the crude oil at 60.degree. F.
(15.56.degree. C.), based on water, using API
gravity=(141.5/p.sub.rel)-131.5.
Determination of oil mobilization and surfactant adsorption rate in
coreflood test
Crude oil (e.g. filtered and viscosity adjustment by addition of
cyclohexane) and synthetic saline water (dissolution of salt,
filtration, adjustment of pH value, salinity determination,
degassing) were prepared before. New sandstone cores were measured
at dry state (mass, pore volume, porosity) and then saturated with
the saline water. Brine permeability was e.g. determined before and
after a tracer test. Then, crude oil was injected at reservoir
temperature and aged.
After oil permeability determination and Soi and Swir calculation,
the cores were flooded with (saline) water. Chemicals were
dissolved in injection water and degassed. Injection of chemicals
followed and effluent was analyzed (collection of oil and water
phase, determination of surfactant retention by HPLC-analysis).
Test results:
The following test results were achieved:
The test results for stability and viscosity of the concentrates
are shown in table 1.
TABLE-US-00002 TABLE 1 Concentrates of anionic surfactant
(A)/anionic surfactant (B) Viscosity at Viscosity at Appearance
20.degree. C. and 50.degree. C. and after storage at Appearance
Surfactant different different 20.degree. C. for 12 after heating
to Ex. concentrate shear rates shear rates weeks 50.degree. C. 1
Concentrate of ca. 3030 mPas 1850 mPas Homogeneous, Homogeneous,
9:1 (by weight) mixture (10 s.sup.-1). (10 s.sup.-1). flowable
liquid flowable liquid of C16C18--7 PO--SO.sub.4Na.sup.a 1900 mPas
1240 mPas at 20.degree. C. and at at 50.degree. C. and at to
C12C14--2 (20 s.sup.-1). (20 s.sup.-1). low shear low shear
EO--SO4Na.sup.b <1000 mPas <<1000 mPas [surfactant content
in (100 s.sup.-1). (100 s.sup.-1). the concentrate was ca. 58% by
weight, content of cosolvent butyl diethylene glycole was ca. 13%
by weight, content of water was ca. 28% by weight, and salt content
was less than 1% by weight].sup.c 2 Concentrate of ca. 830 mPas 290
mPas Homogeneous, Homogeneous, 8:2 (by weight) mixture (10
s.sup.-1). (10 s.sup.-1). flowable liquid easily flowable of
C16C18--7 PO--SO.sub.4Na.sup.a 770 mPas 210 mPas at 20.degree. C.
and at liquid at 50.degree. C. to C12C14--2 (20 s.sup.-1). (20
s.sup.-1). low shear and at low EO--SO4Na.sup.b 690 mPas 190 mPas
shear [surfactant content in (100 s.sup.--1). (100 s.sup.-1). the
concentrate was ca. 78% by weight, content of cosolvent butyl
diethylene glycole was ca. 8% by weight, content of water was ca.
13% by weight, and salt content was less than 1% by weight] 3
Concentrate of ca. 7:3 5000 mPas 3750 mPas Homogeneous,
Homogeneous, (by weight) mixture (10 s.sup.-1). (10 s.sup.-1).
viscous and viscous and of C16C18--7 PO--SO.sub.4Na.sup.a 4000 mPas
2360 mPas flowable liquid flowable liquid to C12C14--2 (20
s.sup.-1). (20 s.sup.-1). at 20.degree. C. at 50.degree. C.
EO--SO4Na.sup.b 2170 mPas 390 mPas [surfactant content in (100
s.sup.-1). (100 s.sup.-1). the concentrate was ca. 77% by weight,
content of cosolvent butyl diethylene glycole was ca. 7% by weight,
content of water was ca. 15% by weight, and salt content was less
than 1% by weight] 4 Concentrate of ca. 6:4 19900 mPas 4110 mPas
Homogeneous, Homogeneous, (by weight) mixture (10 s.sup.-1). (10
s.sup.-1). viscous and viscous and of C16C18--7
PO--SO.sub.4Na.sup.a 11900 mPas 2560 mPas very slow flowable liquid
to C12C14--2 (20 s.sup.-1). (20 s.sup.-1). flowable liquid at
50.degree. C. and at EO--SO4Na.sup.b 3200 mPas <1000 mPas at
20.degree. C. and at low shear [surfactant content in (100
s.sup.-1). (100 s.sup.-1). low shear the concentrate was ca. 69% by
weight, content of water was ca. 30% by weight, and salt content
was less than 1% by weight] C5 Concentrate of 9600 mPas 11960 mPas
Homogeneous, Homogeneous, C16C18--7 PO--SO.sub.4Na.sup.a (10
s.sup.-1). (10 s.sup.-1). viscous and viscous and in water 5810
mPas 8300 mPas very slow very slow [surfactant content in (20
s.sup.-1). (20 s.sup.-1). flowable liquid flowable liquid the
concentrate was 2100 mPas 2500 mPas at 20.degree. C. and at at
50.degree. C. and at ca. 60% by weight, (100 s.sup.-1). (100
s.sup.-1). low shear low shear content of water was ca. 39% by
weight, and salt content was less than 1% by weight] C6 Concentrate
of 6950 mPas 7290 mPas Homogeneous, Homogeneous, C12C14--2
EO--SO.sub.4Na.sup.b (10 s.sup.-1). (10 s.sup.-1). viscous and
viscous and in water 4060 mPas 4670 mPas very slow very slow
[surfactant content in (20 s.sup.-1). (20 s.sup.-1). flowable
liquid flowable liquid the concentrate was 1310 mPas 1350 mPas at
20.degree. C. and at at 50.degree. C. and at ca. 69% by weight,
(100 s.sup.-1). (100 s.sup.-1). low shear low shear content of
water was ca. 30% by weight, and salt content was less than 1% by
weight] .sup.acorresponds to anionic surfactant (A) of general
formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x = 7, y =
0, and M = Na. .sup.bcorresponds to anionic surfactant (B) of
general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with R.sup.2 =
C.sub.12H.sub.25/C.sub.14H.sub.29, z = 2, and M = Na. .sup.cas
described in example 3a) in `Preparation of the mixture comprising
anionic surfactant (A) and anionic surfactant (B)`
As can be seen in table 1 from examples 1 to 3, the claimed
concentrates comprising surfactant mixture of anionic surfactant
(A) and anionic surfactant (B) and the cosolvent butyl diethylene
glycol and water lead to homogeneous flowable liquids at 20.degree.
C. after 12 weeks. Heating-cooling-cycle did not lead to changes.
This is a good indication for robust storage of material e.g. in
remote locations, where additional work for homogenizations means
use of expensive energy. In case of such concentrates and even at
different ratios of anionic surfactant (A) to anionic surfactant
(B), the obtained viscosities were in acceptable range of <5000
mPas for handling/pumping at 20.degree. C. and low shear of 10
s.sup.-1. Increase of shear rate to higher values or increase of
temperature to 50.degree. C. lead to lower values--e.g. <4000
mPas at 50.degree. C. and 10 s.sup.-1 or <1000 mPas at
50.degree. C. and 100 s.sup.-1. This gentle heating for further
viscosity reduction is favored as less energy is needed and such
temperatures do not change surfactant structure. At temperatures of
95.degree. C. for longer time, the viscosity is much lower, but
also the sulfate group might be cleaved due to presence of water.
Example 4 shows a claimed surfactant mixture, but without cosolvent
butyl diethylene glycole. The viscosities are higher compared to
the viscosities in examples 1 to 3. In addition, concentrate in
example 4 is still flowable, but less flowable than the
concentrates in examples 1 to 3, in particular at 50.degree. C.
This shows the benefit of presence of cosolvent such as butyl
diethylene glycol. It is surprising to see, that claimed surfactant
mixture of anionic surfactant (A) and of anionic surfactant (B) in
claimed ratios lead still to a concentrate, which shows at
50.degree. C. lower viscosities at 10, 20 or 100 s.sup.-1 than the
aqueous concentrates of the single surfactants anionic surfactant
(A) in comparative example C5 or anionic surfactant (B) in
comparative example C6: for example at 50.degree. C. and 10
s.sup.-1 one obtained 4110 mPas (example 4) compared to 11960 mPas
(example C5) or compared to 7290 mPas (example C6). In addition,
flow behavior in examples 1-4 at 50.degree. C. and at low shear is
much better compared to the flow behavior in comparative examples
C5 and C6 at 50.degree. C. and at low shear.
In the next chapter the dissolution behavior of the concentrates
described before in saline water are discussed. To a saline water
comprising 26100 ppm of total dissolved salt, fixed amount of
concentrate was given at 20.degree. C. and mixture was stirred at
100 rounds per minute.
TABLE-US-00003 TABLE 2 Test results for dissolution of concentrate
of anionic surfactant (A)/anionic surfactant (B) 0.52% by weight of
Appearance of 0.52% by weight surfactant concentrate of surfactant
concentrate (equals (equals to 0.3% by to 0.3% by weight of active
weight of active material, material, which means the pure which
means the pure surfactants) in 26100 ppm TDS surfactants) in 26100
(20000 ppm Na.sub.2CO.sub.3 combined ppm TDS (20000 ppm with 6100
ppm of salt mixture Na.sub.2CO.sub.3 combined with comprising
mainly NaCl and 6100 ppm of salt mixture NaHCO.sub.3, no
multivalent cations comprising mainly NaCl present) after stirring
with 100 and NaHCO.sub.3, no rpm (rounds per minute) at 20.degree.
C. multivalent cations Ex. Surfactant concentrate for 4 mins
present) 1 Concentrate of ca. 9:1 (by Completely dissolved Clear
solution weight) mixture of C16C18--7 PO--SO.sub.4Na.sup.a to
C12C14--2 EO--SO4Na.sup.b [surfactant content in the concentrate
was ca. 58% by weight, content of cosolvent butyl diethylene
glycole was ca. 13% by weight, content of water was ca. 28% by
weight, and salt content was less than 1% by weight].sup.c
.sup.acorresponds to anionic surfactant (A) of general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x = 7, y =
0, and M = Na. .sup.bcorresponds to anionic surfactant (B) of
general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with R.sup.2 =
C.sub.12H.sub.25/C.sub.14H.sub.29, z = 2, and M = Na. .sup.cas
described in example 3a) in `Preparation of the mixture comprising
anionic surfactant (A) and anionic surfactant (B)`
As can be seen in table 2 from examples 1, the claimed concentrate
comprising claimed surfactant mixture of anionic surfactant (A)
C16C18-7 PO-SO.sub.4Na and anionic surfactant (B) C12C14-2 EO-SO4Na
and the cosolvent butyl diethylene glycole and water can be rapidly
dissolved in a 26100 ppm TDS (total dissolved salt) at 20.degree.
C. A clear solution is obtained.
In addition, solubility tests for different surfactant solutions
are shown in table 3 and table 4. The surfactants can be e.g.
dissolved in the following way, that one volume of saline water
with 6100 ppm TDS comprising 0.6% by weight of dissolved surfactant
formulation is mixed with same volume of saline water with 6100 ppm
TDS comprising 60000 ppm of dissolved Na.sub.2CO.sub.3 at
20.degree. C. (see table 3). Solution is afterwards heated to
62.degree. C.
TABLE-US-00004 TABLE 3 Solubility of different surfactants in
saline water with 36100 ppm TDS (total dissolved salt) at
20.degree. C. and 62.degree. C. Surfactant formulation in saline
water comprising 36100 ppm TDS (30000 ppm Na.sub.2CO.sub.3 combined
with 6100 ppm of salt mixture comprising mainly NaCl and
NaHCO.sub.3, no Appearance at Appearance at Ex. multivalent cations
present) 20.degree. C. 62.degree. C. C1 0.30% by weight of
C16C18--7 PO--SO4Na.sup.a, 0.08% of Clear solution Cloudy and not
weight of butyl diethylene glycole homogeneous solution 2 0.18% by
weight of C16C18--7 PO--SO.sub.4Na.sup.a, 0.12% by Clear solution
Clear solution weight of C12C14--2 EO--SO4Na.sup.b, 0.04% of weight
of butyl diethylene glycole C3 0.15% by weight of C16C18--7BuO--7
PO--15 EO--SO.sub.4Na, Slightly Scattering but 0.15% by weight of
iC13--6 EO--H, 0.09% of scattering homogeneous weight of butyl
diethylene glycole solution solution C4 0.18% by weight of
C16C18--7 PO--SO.sub.4Na.sup.a, 0.12% by Slightly Cloudy and not
weight of iC13--6 EO--H, 0.04% of weight of butyl scattering
homogeneous diethylene glycole solution solution 5 0.18% by weight
of C16C18--22 PO--SO.sub.4Na.sup.c, 0.12% by Clear solution Clear
solution weight of C12C14--2 EO--SO4Na.sup.b 6 0.18% by weight of
C16C18--15 PO--7 EO--SO.sub.4Na.sup.d, Clear solution Clear
solution 0.12% by weight of C12C14--2 EO--SO4Na.sup.b
.sup.acorresponds to anionic surfactant (A) of general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O)y--SO.sub.3-
M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x = 7, y = 0,
and M = Na. .sup.bcorresponds to anionic surfactant (B) of general
formula (II) R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with
R.sup.2 = C.sub.12H.sub.25/C.sub.14H.sub.29, z = 2, and M = Na.
.sup.ccorresponds to anionic surfactant (A) of general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y
--SO.sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x =
22, y = 0, and M = Na. .sup.dcorresponds to anionic surfactant (A)
of general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y
--SO.sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x =
15, y = 7, and M = Na.
As can be seen in table 3 from comparative examples C1, the anionic
surfactant (A) C16C18-7 PO-SO.sub.4Na in presence of cosolvent
butyl diethylene glycole is soluble at 20.degree. C. in saline
water with 36100 ppm TDS but not soluble anymore at 62.degree. C.
In contrast to that, the claimed surfactant mixture of anionic
surfactant (A) C16C18-7 PO-SO.sub.4Na and anionic surfactant (B)
C12C14 -2 EO-SO4Na and of cosolvent butyl diethylene glycole gives
under same conditions a much better behavior as shown in example 2:
at 20.degree. C. and at 62.degree. C. a clear solution is obtained.
Comparative example C3 shows a different surfactant system
comprising an anionic surfactant C16C18-7BuO-7PO-15EO-SO4Na (from
prior art WO 11110503 A1) and a nonionic surfactant iC13-6EO-H
(equals to Lutensol.RTM. TO6 from BASF). Observed solution behavior
is not ideal, but acceptable: at 20.degree. C. and at 62.degree. C.
scattering but homogeneous solutions were obtained. Comparative
example C4 shows, that the combination of anionic surfactant (A)
C16C18-7 PO-SO.sub.4Na with the nonionic surfactant iC13-6EO-H
(equals to Lutensol.RTM. TO6 from BASF) is inferior compared to
claimed surfactant mixture described in example 2: while in example
2 clear solution was obtained at 62.degree. C., a cloudy and not
homogeneous solution was observed in example C4. Injection of a
cloudy and not homogeneous solution would lead to separation of
material (surfactant could not pump to the oil, but would stuck in
the formation) and could even plug the injection area. Example 5
and 6 show, that also other claimed surfactant mixtures lead to
clear solutions at 36100 ppm TDS and at 20.degree. C. or 62.degree.
C.: anionic surfactant (A) C16C18-22 PO-SO4Na and anionic
surfactant (B) C12C14-2 EO-SO4Na or anionic surfactant (A)
C16C18-15 PO-7 EO-SO4Na and anionic surfactant (B) C12C14-2
EO-SO4Na give clear solutions.
TABLE-US-00005 TABLE 4 Solubility of different surfactants in
saline water with 26100 ppm TDS (total dissolved salt) at
20.degree. C. and 62.degree. C. Surfactant formulation in saline
water comprising 26100 ppm TDS (20000 ppm Na.sub.2CO.sub.3 combined
with 6100 ppm of salt mixture comprising mainly NaCl and
NaHCO.sub.3, no Appearance at Appearance at Ex. multivalent cations
present) 20.degree. C. 62.degree. C. 1 0.27% by weight of C16C18
--7 PO--SO.sub.4Na.sup.a, 0.03% by Clear solution Clear solution
weight of C12C14--2 EO--SO4Na.sup.b, 0.07% of weight of butyl
diethylene glycole 2 0.18% by weight of C16C18--7
PO--SO.sub.4Na.sup.a, 0.12% by Clear solution Clear solution weight
of C12C14--2 EO--SO4Na.sup.b, 0.04% of weight of butyl diethylene
glycole C3 0.18% by weight of C16C18--7 PO--SO.sub.4Na.sup.a, 0.12%
by Clear solution Cloudy and not weight of iC13--6 EO--H, 0.04% of
weight of butyl homogeneous diethylene glycole solution
.sup.acorresponds to anionic surfactant (A) of general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x = 7, y =
0, and M = Na. .sup.bcorresponds to anionic surfactant (B) of
general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with R.sup.2 =
C.sub.12H.sub.25/C.sub.14H.sub.29, z = 2, and M = Na.
As can be seen in table 4 from examples 1 and 2, the claimed
surfactant mixture of anionic surfactant (A) C16C18-7 PO-SO4Na and
anionic surfactant (B) C12C14-2 EO-SO4Na and of cosolvent butyl
diethylene glycole gives also at lower salinity (26100 ppm TDS in
table 4 compared to 36100 ppm TDS in table 3) a good solubility
behavior: at 20.degree. C. and at 62.degree. C. a clear solution is
obtained. Comparative example C3 shows, that the combination of
anionic surfactant (A) C16C18-7 PO-SO4Na with the nonionic
surfactant iC13-6EO-H (equals to Lutensol.RTM. TO6 from BASF) is
inferior compared to claimed surfactant mixture described in
example 2: while in example 2 clear solution was obtained at
62.degree. C., a cloudy and not homogeneous solution was observed
in example C4. Injection of a cloudy and not homogeneous solution
would lead to separation of material (surfactant could not pump to
the oil, but would stuck in the formation) and could even plug the
injection area.
In the next chapter, reduction of interfacial tension between
saline water and crude oil is investigated (see table 5). A crude
oil, which is rich in paraffin and solidifies at 50.degree. C. is
used. API degree of crude oil is <29. Measurements (spinning
drop method) are done at reservoir temperature of 62.degree. C.
TABLE-US-00006 TABLE 5 Interfacial tensions against crude oil in
the presence of anionic surfactant (A)/anionic surfactant (B)
Surfactant solubility in the salt IFT at solution at Example
Surfactant formulation Salt solution 62.degree. C. 62.degree. C. 1
0.18% by weight of C16C18--7 30000 ppm Na.sub.2CO.sub.3 0.002 Clear
PO--SO.sub.4Na.sup.a, 0.12% by weight combined with 6100 ppm mN/m
soluble of C12C14--2 EO--SO4Na.sup.b, of salt mixture comprising
0.04% of weight of mainly NaCl and NaHCO.sub.3, butyl diethylene
glycole no multivalent cations present 2 0.27% by weight of
C16C18--7 20000 ppm Na.sub.2CO.sub.3 0.004 Clear
PO--SO.sub.4Na.sup.a, 0.03% by weight combined with 6100 ppm mN/m
soluble of C12C14--2 EO-- SO4Na.sup.b, of salt mixture comprising
0.07% of weight of mainly NaCl and NaHCO.sub.3, butyl diethylene
glycole no multivalent cations present 3 0.27% by weight of
C16C18--7 15000 ppm Na.sub.2CO.sub.3 0.007 Clear
PO--SO.sub.4Na.sup.a, 0.03% by weight combined with 6100 ppm mN/m
soluble of C12C14--2 EO--SO4Na.sup.b, of salt mixture comprising
0.07% of weight of mainly NaCl and NaHCO.sub.3, butyl diethylene
glycole no multivalent cations present 4 0.12% by weight of
C16C18--7 25000 ppm Na.sub.2CO.sub.3 0.006 Clear
PO--SO.sub.4Na.sup.a, 0.08% by weight combined with 6100 ppm mN/m
soluble of C12C14--2 EO--SO4Na.sup.b, of salt mixture comprising
0.03% of weight of mainly NaCl and NaHCO.sub.3, butyl diethylene
glycole no multivalent cations present 5 0.18% by weight of
C16C18--7 25000 ppm Na.sub.2CO.sub.3 0.001 Clear
PO--SO.sub.4Na.sup.a, 0.02% by weight combined with 6100 ppm mN/m
soluble of C12C14--2 EO--SO4Na.sup.b, of salt mixture comprising
0.05% of weight of mainly NaCl and NaHCO.sub.3, butyl diethylene
glycole no multivalent cations present 6 0.18% by weight of
C16C18--7 20000 ppm Na.sub.2CO.sub.3 0.003 Clear
PO--SO.sub.4Na.sup.a, 0.02% by weight combined with 6100 ppm mN/m
soluble of C12C14--2 EO--SO4Na.sup.b, of salt mixture comprising
0.05% of weight of mainly NaCl and NaHCO.sub.3, butyl diethylene
glycole no multivalent cations present .sup.acorresponds to anionic
surfactant (A) of general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x = 7, y =
0, and M = Na. .sup.bcorresponds to anionic surfactant (B) of
general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with R.sup.2 =
C.sub.12H.sub.25/C.sub.14H.sub.29, z = 2, and M = Na.
As can be seen in table 5 from examples 1 to 6, the claimed
surfactant mixture of anionic surfactant (A) C16C18-7 PO-SO4Na and
anionic surfactant (B) C12C14-2 EO-SO4Na and of cosolvent butyl
diethylene glycole gives at different salinities (15000 -30000 ppm
Na.sub.2CO.sub.3 combined with 6100 ppm salt mixture comprising
mainly NaCl and NaHCO3, no multivalent cations present), at
different surfactant ratio (9:1 or 6:4 by weight of anionic
surfactant (A) to anionic surfactant (B); example 2,3,5 and 6
compared to example 1 and 4), and at different concentration (0.2%
to 0.3% by weight of anionic surfactant (A) to anionic surfactant
(B); example 4-6 compared to example 1 -3) a desired ultralow
interfacial tension of <0.01 mN/m at 62.degree. C. In addition,
all surfactant solutions are clear soluble at 62.degree. C. in
described saline waters.
Finally, core flood tests with sandstone cores were done in order
to determine oil mobilization rate and adsorption rate of described
surfactant formulations in presence of anionic polyacrylamide
(aPAM; aPAM is used for for mobility control). Bentheimer sandstone
cores (12.01 in.times.1.49 in; porosity 24%; 82 ml pore volume)
were used for core flood tests at 62.degree. C. The cores were
saturated with saline water. Brine permeability (with use of
tracer) was determined: ca. 2100 mD for all the cores. Crude oil
(rich in paraffin) was injected into the cores at 62.degree. C. and
aged. Then, water flooding was started. The water recovery
efficiency (amount of oil produced by water flooding) was in all
cores in a very similar range: 53-58% original oil in place.
Alkali-surfactant-polymer slug (0.3 pore volume) were injected,
followed by alkali-polymer slugs. Table 6 shows the results for
different surfactant formulations.
TABLE-US-00007 TABLE 6 Oil mobilization rate and adsorption rate of
surfactant formulations in presence of aPAM (3000 ppm) at
62.degree. C. in sandstone core comprising crude oil rich in
paraffin and saline water Cumulative Surfactant oil Example
Surfactant formulation Salt solution adsorption recovered 1 0.18%
by weight of C16C18--7 30000 ppm Na.sub.2CO.sub.3 0.036 mg 97.9%
PO--SO.sub.4Na.sup.a, 0.12% by combined with 6100 ppm surfactant
original weight of C12C14--2 EO--SO4Na.sup.b, of salt mixture
comprising per g rock oil in place 0.04% of weight of mainly NaCl
and NaHCO.sub.3, butyl diethylene glycole no multivalent cations
present 2 0.27% by weight of C16C18--7 20000 ppm Na.sub.2CO.sub.3
0.035 mg 98.4% PO--SO.sub.4Na.sup.a, 0.03% by combined with 6100
ppm surfactant original weight of C12C14--2 EO--SO4Na.sup.b, of
salt mixture comprising per g rock oil in place 0.07% of weight of
mainly NaCl and NaHCO.sub.3, butyl diethylene glycole no
multivalent cations present 3 0.18% by weight of C16C18--7 20000
ppm Na.sub.2CO.sub.3 0.026 mg 97.5% PO--SO.sub.4Na.sup.a, 0.02% by
combined with 6100 ppm surfactant original weight of C12C14--2
EO--SO4Na.sup.b, of salt mixture comprising per g rock oil in place
0.05% of weight of mainly NaCl and NaHCO.sub.3, butyl diethylene
glycole no multivalent cations present C4 0.15% by weight of
C16C18--7BuO--7 20000 ppm Na.sub.2CO.sub.3 0.104 mg 80.3% PO--15
EO--SO.sub.4Na, combined with 6100 ppm surfactant original 0.15% by
weight of of salt mixture comprising per g rock oil in place
iC13--6 EO--H, 0.09% of mainly NaCl and NaHCO.sub.3, weight of
butyl diethylene no multivalent cations glycole present
.sup.acorresponds to anionic surfactant (A) of general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x = 7, y =
0, and M = Na. .sup.bcorresponds to anionic surfactant (B) of
general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with R.sup.2 =
C.sub.12H.sub.25/C.sub.14H.sub.29, z = 2, and M = Na.
As can be seen in table 6 from examples 1 to 3, the claimed
surfactant mixture of anionic surfactant (A) C16C18-7 -PO-SO4Na and
anionic surfactant (B) C12C14-2 EO-SO4Na and of cosolvent butyl
diethylene glycole gives at different salinities (20000-30000 ppm
Na.sub.2CO.sub.3 combined with 6100 ppm salt mixture comprising
mainly NaCl and NaHCO.sub.3, no multivalent cations present), at
different surfactant ratio (9:1 or 6:4 by weight of anionic
surfactant (A) to anionic surfactant (B); example 2-3 compared to
example 1), and at different concentration (0.2% to 0.3% by weight
of anionic surfactant (A) to anionic surfactant (B); example 3
compared to example 1-2) a surprisingly high cumulative oil
recovery (total volume of oil recovered) of .gtoreq.97.5% original
oil in place. At the same time, the surfactant adsorption rate is
with <0.05 mg per g rock astonishingly low. Comparative example
C4 shows a different surfactant system comprising an anionic
surfactant C16C18-7BuO-7PO-15EO-SO4Na (from prior art WO 11110503
A1) and a nonionic surfactant iC13-6EO-H (equals to Lutensol.RTM.
TO6 from BASF). The results are good (0.1 mg surfactant per g rock
adsorbed, cumulative oil recovery in range of 80% original oil in
place), but inferior compared to surprisingly good results from
example 1-3. Lower surfactant adsorption rate and higher cumulative
oil recovery are beneficial to make the chemical enhanced oil
recovery process more economic and more attractive for the
operator.
Not shown in table 6 is the ASP incremental oil recovery
(additional oil recovered at one pore volume after
alkali-surfactant-polymer injection end): Example 1: 36.4% original
oil in place Example 2: 40.0% original oil in place Example 3:
40.6% original oil in place Comparative example C4:19.8% original
oil in place
This shows, that in example 1-3 huge majority of the oil mobilized
by chemicals is obtained within first pore volume. This beneficial
for an operator (fast oil production, fast return on investment).
In comparative example C4, a significant amount of oil is obtained
later.
In the following, comparison examples are provided in view of the
teaching of US 2016/0215200 A1. In paragraph [0129] of US
2016/0215200 A1, it is mentioned that "a hydrocarbon recovery
composition may include an inorganic salt (e.g. sodium carbonate
(Na2CO3), sodium chloride (NaCl), or calcium chloride
(CaCl.sub.2))". In claim 13 of US 2016/0215200 A1 it is described,
that "the brine has a hardness of at least 0.5 wt %". In table 2 of
US 2016/0215200 A1, a synthetic sea water is described, which
comprises 2.7 weight-% NaCl, 0.13 weight-% CaCl.sub.2, 1.12
weight-% MgCl.sub.2.times.6 H.sub.2O, and 0.48 weight-%
Na.sub.2SO.sub.4, which were used for the tests described in US
2016/0215200 A1.
Synthetic sea water from table 2 of US 2016/0215200 A1 without
Na.sub.2CO.sub.3 at 20.degree. C. was prepared and was clear,
whereas addition of 20000 ppm Na.sub.2CO.sub.3 at 20.degree. C.
immediately led to a clouding. After a storage time of 44 h at
20.degree. C. a massive precipitate occurred, when sodium carbonate
was combined with synthetic sea water and stored for roughly 2
days.
Such a clouding or precipitation is very critical as it can plug
the porous reservoir, which can negatively affect the oil
production. US 2016/0215200 A1 does not teach, how to overcome such
a clouding or precipitation.
US 2016/0215200 A1 describes the combination of an alkyl propoxy
sulfate with a second anionic surfactant out of the group of alkyl
propoxy ethoxy sulfate or out of the group of alkyl ethoxy sulfate.
In chapter [0056] of US 2016/0215200 it is described, that the
second anionic surfactant should most preferably comprises at least
6 alkoxy units. In chapter [0057] of US 2016/0215200 A1 it is
described, that the number of alkoxy units should not to be too
small. In table 4 and table 5 of US 2016/0215200 A1, alkyl ethoxy
sulfates with 7 ethoxy units are described (iC13-7 EO-Sulfate and
C12C13-7 EO-Sulfate). They were combined with the alkyl propoxy
sulfate C16C17-7 PO-Sulfate. Chapter [0151] and table 5 of US
2016/0215200 A1 show, that these combinations (C16C17-7 PO-Sulfate
with iC13-7 EO-Sulfate or C16C17-7 PO-Sulfate with C12C13-7
EO-Sulfate) are used at concentrations of at least 1 weight-%, at
room temperature and in synthetic sea water. It was claimed, that
these are the optimal blends. For a higher salinity (2.times.
seawater) such combinations did not provide optimal blends at room
temperature as shown in table 5 of US 2016/0215200 A1. Chapter
[0160] of US 2016/0215200 A1 shows, that ata higher temperature of
50.degree. C. a different surfactant combination C12C13 -7
PO-Sulfate and C12C13-7 EO-Sulfate (ratio 83:17) was chosen to be
an optimum blend (see example 2 of US 2016/0215200: 0.6 wt %
surfactant concentration was used and salinities around sea water
were screened in phase behavior tests with crude oil at 50.degree.
C.).
According to the description within claim 1 of US 2016/0215200 A1
following surfactants were synthesized and compared: iC16-7
PO-Sulfate (iC16 is alkyl moiety 2-hexyldecyl and has a branching
degree of 1) iC12-7 PO-Sulfate (iC12 is alkyl moiety 2-butyloctyl
and has a branching degree of 1) iC12-7 EO-Sulfate (iC12 is alkyl
moiety 2-butyloctyl and has a branching degree of 1)
The reduction of interfacial tension between saline water and crude
oil is investigated (see table 7). A crude oil, which is rich in
paraffin and solidifies at 50.degree. C. is used. API degree of
crude oil is <29. Measurements (spinning drop method) are done
at reservoir temperature of 62.degree. C.
TABLE-US-00008 TABLE 7 Interfacial tensions against crude oil in
the presence of anionic surfactant (A)/anionic surfactant (B) and
comparison with surfactants claimed by US 2016/0215200 A1
Surfactant solubility in the salt IFT at solution at Example
Surfactant formulation Salt solution 62.degree. C. 62.degree. C. C1
0.255% by weight of iC16--7 Synthetic seawater as Not Very
PO--SO.sub.4Na, 0.045% by described in table 2 of determined due
scattering weight of iC12--7 EO--SO4Na US 2016/0215200 to
solubility till slight issues clouding C2 0.15% by weight of
iC16--7 Synthetic seawater as 0.187 Clear soluble PO--SO.sub.4Na,
0.15% by described in table 2 of mN/m weight of iC12--7 EO--SO4Na
US 2016/0215200 C3 0.15% by weight of iC16--7 Synthetic seawater as
0.225 Clear soluble PO--SO.sub.4Na, 0.15% by described in table 2
of US mN/m weight of iC12--7 EO--SO4Na 2016/0215200 diluted with
distilled water to a salinity of 31100 ppm TDS C4 0.25% by weight
of iC12--7 Synthetic seawater as 0.168 Clear soluble
PO--SO.sub.4Na, 0.05% by described in table 2 of mN/m weight of
iC12--7 EO--SO4Na US 2016/0215200 5 0.18% by weight of C16C18--7
25000 ppm Na.sub.2CO.sub.3 combined 0.001 Clear soluble
PO--SO.sub.4Na.sup.a, 0.02% by weight with 6100 ppm of salt mN/m of
C12C14--2 EO--SO4Na.sup.b, mixture comprising mainly 0.05% of
weight of NaCl and NaHCO.sub.3, no butyl diethylene glycole
multivalent cations present C6 0.25% by weight of iC12--7 25000 ppm
Na.sub.2CO.sub.3 combined 0.118 Clear soluble PO--SO.sub.4Na, 0.05%
by weight with 6100 ppm of salt mN/m of iC12--7 EO--SO4Na mixture
comprising mainly NaCl and NaHCO.sub.3, no multivalent cations
present .sup.acorresponds to anionic surfactant (A) of general
formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x = 7, y =
0, and M = Na. .sup.bcorresponds to anionic surfactant (B) of
general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with R.sup.2 =
C.sub.12H.sub.25/C.sub.14H.sub.29, z = 2, and M = Na.
As shown in table 7 only surfactant formulation described in
example 5 provided a desired ultralow interfacial tension against
the crude oil at 62.degree. C. The other comparative examples C1-C4
and C6 comprise surfactant formulations claimed in US 2016/0215200
A1. Investigations were started with synthetic seawater described
in US 2016/0215200 A1. As shown in comparative example C1, 3000 ppm
of a 85:15 ratio of iC16-7P-Sulfate to iC12-7 EO-Sulfate was not
sufficient soluble at 62.degree. C. There ratio was changed to 1:1
and clear solution was obtained (see C2), but interfacial tension
remained above 0.1 mN/m. A reduction in salinity to 31100 ppm TDS
(see C3) did not improve reduction of interfacial tension further.
Another surfactant combination claimed by US 2016/0215200 A1 was
used as it was used at elevated temperatures: 3000 ppm of a 83:17
ratio of iC12-7PO-Sulfate to iC12-7 EO-Sulfate. In contrast to
comparative example C1, such surfactant formulation with an excess
of the alkyl propoxy sulfate--used in comparative example C4--did
not have solubility issues. However, interfacial tension remained
still above 0.1 mN/m. However, another trial was started and
Na.sub.2CO.sub.3 was used instead of the synthetic seawater. As
shown in comparative example C6, the interfacial tension reduction
was improved only slightly and remained above 0.1 mN/m. Under
identical conditions, the claimed surfactant formulation of this
intellectual property described in example 5 led to the desired
results.
In addition, further surfactants were synthesized and tested. The
reduction of interfacial tension between saline water and crude oil
is investigated (see table 8). A crude oil, which is rich in
paraffin and solidifies at 50.degree. C. is used. API degree of
crude oil is <29. Measurements (spinning drop method) are done
at reservoir temperature of 62.degree. C. and values noted (e.g.
after 1 h).
TABLE-US-00009 TABLE 8 Interfacial tensions against crude oil in
the presence of anionic surfactant (A)/anionic surfactant (B)
Surfactant solubility in the salt IFT at solution at Example
Surfactant formulation Salt solution 62.degree. C. 62.degree. C. 1
0.27% by weight of C16C18--7 25000 ppm Na.sub.2CO.sub.3 combined
0.005 Clear soluble PO--SO.sub.4Na.sup.a, 0.03% by weight with 6100
ppm of salt mN/m of C12C14--4 EO--SO4Na.sup.f, mixture comprising
mainly 0.07% of weight of NaCl and NaHCO.sub.3, no butyl diethylene
glycole multivalent cations present 2 0.27% by weight of C16C18--7
25000 ppm Na.sub.2CO.sub.3 combined 0.004 Clear soluble PO--5
EO--SO.sub.4Na.sup.e, with 6100 ppm of salt mN/m 0.03% by weight of
C12C14--2 mixture comprising mainly EO--SO4Na.sup.b, 0.07% of NaCl
and NaHCO.sub.3, no weight of butyl diethylene multivalent cations
present glycole 3 0.18% by weight of C16C18--7 25000 ppm
Na.sub.2CO.sub.3 combined 0.006 Clear soluble PO--SO.sub.4Na.sup.a,
0.02% by weight with 6100 ppm of salt mN/m of C12C14--4
EO--SO4Na.sup.f, mixture comprising mainly 0.05% of weight of NaCl
and NaHCO.sub.3, no butyl diethylene glycole multivalent cations
present 4 0.18% by weight of C16C18--7 25000 ppm Na.sub.2CO.sub.3
combined 0.003 Clear soluble PO--5 EO--SO.sub.4Na.sup.e, with 6100
ppm of salt mN/m 0.02% by weight of C12C14--2 mixture comprising
mainly EO--SO4Na.sup.b, 0.05% of NaCl and NaHCO.sub.3, no weight of
butyl diethylene multivalent cations present glycole
.sup.acorresponds to anionic surfactant (A) of general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x = 7, y =
0, and M = Na. .sup.bcorresponds to anionic surfactant (B) of
general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with R.sup.2 =
C.sub.12H.sub.25/C.sub.14H.sub.29, z = 2, and M = Na.
.sup.ecorresponds to anionic surfactant (A) of general formula (I)
R.sup.1--O--(CH.sub.2C(CH.sub.3)HO).sub.x--(CH.sub.2CH.sub.2O).sub.y--SO.-
sub.3M with R.sup.1 = C.sub.16H.sub.33/C.sub.18H.sub.37, x = 7, y =
5, and M = Na. .sup.fcorresponds to anionic surfactant (B) of
general formula (II)
R.sup.2--O--(CH.sub.2CH.sub.2O).sub.z--SO.sub.3M with R.sup.2 =
C.sub.12H.sub.25/C.sub.14H.sub.29, z = 4, and M = Na
As shown in table 8 several other claimed surfactant combinations
gave clear solutions under reservoir conditions and led to ultralow
interfacial tension values in presence of crude oil (example 1-4:
0.003-0.006 mN/m) at low surfactant concentrations <<1 wt %
(example 1-4: 0.2-0.3 wt %). Compared to surfactant combinations
from table 5, anionic surfactant (A) of general formula (I) has an
additional EO block (example 2 and 4: y=5) or anionic surfactant
(B) of general formula (II) has a longer EO block (example 1 and 3:
z=4). This demonstrates, that a broader range of surfactants can be
used.
* * * * *